Klystron

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Klystron 

400 kW klystron used for spacecraft communication at the Canberra Deep Space Communications Complex. This is a spare in storage.

 

5 kW klystron tube used as power amplifier in UHF television transmitter, 1952. When installed, the tube projects through holes in the center of the cavity resonators, with the sides of the cavities making contact with the metal rings on the tube.

A klystron is a specialized linear-beam vacuum tube, invented in 1937 by American electrical engineers Russell and Sigurd Varian, which is used as an amplifier for high radio frequencies, from UHF up into the microwave range. Low-power klystrons are used as oscillators in terrestrial microwave relay communications links, while high-power klystrons are used as output tubes in UHF television transmitters, satellite communication, radar transmitters, and to generate the drive power for modern particle accelerators.

In a klystron, an electron beam interacts with radio waves as it passes through resonant cavities, metal boxes along the length of a tube. The electron beam first passes through a cavity to which the input signal is applied. The energy of the electron beam amplifies the signal, and the amplified signal is taken from a cavity at the other end of the tube. The output signal can be coupled back into the input cavity to make an electronic oscillator to generate radio waves. The gain of klystrons can be high, 60 dB (an increase in signal power by a factor of one million) or more, with output power up to tens of megawatts, but the bandwidth is narrow, usually a few percent although it can be up to 10% in some devices.

A reflex klystron is an obsolete type in which the electron beam was reflected back along its path by a high potential electrode, used as an oscillator.

The name klystron comes from the Greek verb κλύζω (klyzo) referring to the action of waves breaking against a shore, and the suffix -τρον ("tron") meaning the place where the action happens. The name "klystron" was suggested by Hermann Fränkel, a professor in the classics department at Stanford University when the klystron was under development.

History

The first commercial klystron, manufactured by Westinghouse in 1940. Part of the tube is cut away to show the internal construction. On the left are the cathode and accelerating anode, which create the electron beam. In the center between the wooden supports is the drift tube, surrounded by the two donut-shaped cavity resonators: the "buncher" and the "catcher". The output terminal is visible at top. On the right is the cone shaped collector anode, which absorbs the electrons. It could generate 200 W of power at a wavelength of 40 centimeters (750 MHz) with 50% efficiency.

The klystron was the first significantly powerful source of radio waves in the microwave range; before its invention the only sources were the Barkhausen-Kurz tube and split anode magnetron, which were limited to very low power. It was invented by the brothers Russell and Sigurd Varian at Stanford University. Their prototype was completed and demonstrated successfully on August 30, 1937. Upon publication in 1939, news of the klystron immediately influenced the work of US and UK researchers working on radar equipment. The Varians went on to found Varian Associates to commercialize the technology (for example, to make small linear accelerators to generate photons for external beam radiation therapy). Their work was preceded by the description of velocity modulation by A. Arsenjewa-Heil and Oskar Heil (wife and husband) in 1935, though the Varians were probably unaware of the Heils' work.

The work of physicist W.W. Hansen was instrumental in the development of the klystron and was cited by the Varian brothers in their 1939 paper. His resonator analysis, which dealt with the problem of accelerating electrons toward a target, could be used just as well to decelerate electrons (i.e., transfer their kinetic energy to RF energy in a resonator). During the second World War, Hansen lectured at the MIT Radiation labs two days a week, commuting to Boston from Sperry Gyroscope Company on Long Island. His resonator was called a "rhumbatron" by the Varian brothers. Hansen died of beryllium disease in 1949 as a result of exposure to beryllium oxide (BeO).

During the Second World War, the Axis powers relied mostly on (then low-powered and long wavelength) klystron technology for their radar system microwave generation, while the Allies used the far more powerful but frequency-drifting technology of the cavity magnetron for much shorter-wavelength centimetric microwave generation. Klystron tube technologies for very high-power applications, such as synchrotrons and radar systems, have since been developed.

Right after the war, AT&T used 4 watt klystrons in its brand new network of microwave relay links that covered the US continent. The network provided long-distance telephone service and also carried television signals for the major TV networks. Western Union Telegraph Company also built point-to-point microwave communication links using intermediate repeater stations at about 40 mile intervals at that time, using 2K25 reflex klystrons in both the transmitters and receivers.

Operation

Klystrons amplify RF signals by converting the kinetic energy in a DC electron beam into radio frequency power. In a vacuum, a beam of electrons is emitted by an electron gun or thermionic cathode and accelerated by high-voltage electrodes (typically in the tens of kilovolts).

This beam passes through an input cavity resonator. RF energy has been fed into the input cavity at, or near, its resonant frequency, creating standing waves, which produce an oscillating voltage, which acts on the electron beam. The electric field causes the electrons to "bunch": electrons that pass through when the electric field opposes their motion are slowed, while electrons which pass through when the electric field is in the same direction are accelerated, causing the previously continuous electron beam to form bunches at the input frequency.

To reinforce the bunching, a klystron may contain additional "buncher" cavities.

The beam then passes through a "drift" tube, in which the faster electrons catch up to the slower ones, creating the "bunches", then through a "catcher" cavity.

In the output "catcher" cavity, each bunch enters the cavity at the time in the cycle when the electric field opposes the electrons' motion, decelerating them. Thus the kinetic energy of the electrons is converted to potential energy of the field, increasing the amplitude of the oscillations. The oscillations excited in the catcher cavity are coupled out through a coaxial cable or waveguide.

The spent electron beam, with reduced energy, is captured by a collector electrode.

To make an oscillator, the output cavity can be coupled to the input cavity(s) with a coaxial cable or waveguide. Positive feedback excites spontaneous oscillations at the resonant frequency of the cavities.

Two-cavity klystron

The simplest klystron tube is the two-cavity klystron. In this tube there are two microwave cavity resonators, the "catcher" and the "buncher". When used as an amplifier, the weak microwave signal to be amplified is applied to the buncher cavity through a coaxial cable or waveguide, and the amplified signal is extracted from the catcher cavity.

At one end of the tube is the hot cathode which produces electrons when heated by a filament. The electrons are attracted to and pass through an anode cylinder at a high positive potential; the cathode and anode act as an electron gun to produce a high velocity stream of electrons. An external electromagnet winding creates a longitudinal magnetic field along the beam axis which prevents the beam from spreading.

The beam first passes through the "buncher" cavity resonator, through grids attached to each side. The buncher grids have an oscillating AC potential across them, produced by standing wave oscillations within the cavity, excited by the input signal at the cavity's resonant frequency applied by a coaxial cable or waveguide. The direction of the field between the grids changes twice per cycle of the input signal. Electrons entering when the entrance grid is negative and the exit grid is positive encounter an electric field in the same direction as their motion, and are accelerated by the field. Electrons entering a half-cycle later, when the polarity is opposite, encounter an electric field which opposes their motion, and are decelerated.

Beyond the buncher grids is a space called the drift space. This space is long enough so that the accelerated electrons catch up with electrons that were decelerated at an earlier time, forming "bunches" longitudinally along the beam axis. Its length is chosen to allow maximum bunching at the resonant frequency, and may be several feet long.

Klystron oscillator from 1944. The electron gun is on the right, the collector on the left. The two cavity resonators are in center, linked by a short coaxial cable to provide positive feedback.

The electrons then pass through a second cavity, called the "catcher", through a similar pair of grids on each side of the cavity. The function of the catcher grids is to absorb energy from the electron beam. The bunches of electrons passing through excite standing waves in the cavity, which has the same resonant frequency as the buncher cavity. Each bunch of electrons passes between the grids at a point in the cycle when the exit grid is negative with respect to the entrance grid, so the electric field in the cavity between the grids opposes the electrons motion. The electrons thus do work on the electric field, and are decelerated, their kinetic energy is converted to electric potential energy, increasing the amplitude of the oscillating electric field in the cavity. Thus the oscillating field in the catcher cavity is an amplified copy of the signal applied to the buncher cavity. The amplified signal is extracted from the catcher cavity through a coaxial cable or waveguide.

After passing through the catcher and giving up its energy, the lower energy electron beam is absorbed by a "collector" electrode, a second anode which is kept at a small positive voltage.

Klystron oscillator

An electronic oscillator can be made from a klystron tube, by providing a feedback path from output to input by connecting the "catcher" and "buncher" cavities with a coaxial cable or waveguide. When the device is turned on, electronic noise in the cavity is amplified by the tube and fed back from the output catcher to the buncher cavity to be amplified again. Because of the high Q of the cavities, the signal quickly becomes a sine wave at the resonant frequency of the cavities.

Multicavity klystron

In all modern klystrons, the number of cavities exceeds two. Additional "buncher" cavities added between the first "buncher" and the "catcher" may be used to increase the gain of the klystron or to increase the bandwidth.

The residual kinetic energy in the electron beam when it hits the collector electrode represents wasted energy, which is dissipated as heat, which must be removed by a cooling system. Some modern klystrons include depressed collectors, which recover energy from the beam before collecting the electrons, increasing efficiency. Multistage depressed collectors enhance the energy recovery by "sorting" the electrons in energy bins.

Reflex klystron

Low-power Soviet reflex klystron from 1963. The cavity resonator from which the output is taken, is attached to the electrodes labeled Externer Resonator. Reflex klystrons are almost obsolete now.

 

cutaway: reflex klystron

 

Main article: Sutton tube

The reflex klystron (also known as a Sutton tube after one of its inventors, Robert Sutton) was a low power klystron tube with a single cavity, which functioned as an oscillator. It was used as a local oscillator in some radar receivers and a modulator in microwave transmitters the 1950s and 1960s, but is now obsolete, replaced by semiconductor microwave devices.

In the reflex klystron the electron beam passes through a single resonant cavity. The electrons are fired into one end of the tube by an electron gun. After passing through the resonant cavity they are reflected by a negatively charged reflector electrode for another pass through the cavity, where they are then collected. The electron beam is velocity modulated when it first passes through the cavity. The formation of electron bunches takes place in the drift space between the reflector and the cavity. The voltage on the reflector must be adjusted so that the bunching is at a maximum as the electron beam re-enters the resonant cavity, thus ensuring a maximum of energy is transferred from the electron beam to the RF oscillations in the cavity. The reflector voltage may be varied slightly from the optimum value, which results in some loss of output power, but also in a variation in frequency. This effect is used to good advantage for automatic frequency control in receivers, and in frequency modulation for transmitters. The level of modulation applied for transmission is small enough that the power output essentially remains constant. At regions far from the optimum voltage, no oscillations are obtained at all. There are often several regions of reflector voltage where the reflex klystron will oscillate; these are referred to as modes. The electronic tuning range of the reflex klystron is usually referred to as the variation in frequency between half power points—the points in the oscillating mode where the power output is half the maximum output in the mode.

Modern semiconductor technology has effectively replaced the reflex klystron in most applications.

Gyroklystron

The gyroklystron is a microwave amplifier with operation dependent on the cyclotron resonance condition. Similarly to the klystron, its operation depends on the modulation of the electron beam, but instead of axial bunching the modulation forces alter the cyclotron frequency and hence the azimuthal component of motion, resulting in phase bunches. In the output cavity, electrons which arrive at the correct decelerating phase transfer their energy to the cavity field and the amplified signal can be coupled out. The gyroklystron has cylindrical or coaxial cavities and operates with transverse electric field modes. Since the interaction depends on the resonance condition, larger cavity dimensions than a conventional klystron can be used. This allows the gyroklystron to deliver high power at very high frequencies which is challenging using conventional klystrons.

Tuning

Large klystrons as used in the storage ring of the Australian Synchrotron to maintain the energy of the electron beam

Some klystrons have cavities that are tunable. By adjusting the frequency of individual cavities, the technician can change the operating frequency, gain, output power, or bandwidth of the amplifier. No two klystrons are exactly identical (even when comparing like part/model number klystrons). Each unit has manufacturer-supplied calibration values for its specific performance characteristics. Without this information the klystron would not be properly tunable, and hence not perform well, if at all.

Tuning a klystron is delicate work which, if not done properly, can cause damage to equipment or injury to the technician due to the very high voltages that could be produced. The technician must be careful not to exceed the limits of the graduations, or damage to the klystron can result. Other precautions taken when tuning a klystron include using nonferrous tools. Some klystrons employ permanent magnets. If a technician uses ferrous tools (which are ferromagnetic) and comes too close to the intense magnetic fields that contain the electron beam, such a tool can be pulled into the unit by the intense magnetic force, smashing fingers, injuring the technician, or damaging the unit. Special lightweight nonmagnetic (or rather very weakly diamagnetic) tools made of beryllium alloy have been used for tuning U.S. Air Force klystrons.

Precautions are routinely taken when transporting klystron devices in aircraft, as the intense magnetic field can interfere with magnetic navigation equipment. Special overpacks are designed to help limit this field "in the field," and thus allow such devices to be transported safely.

Optical klystron

The technique of amplification used in the klystron is also being applied experimentally at optical frequencies in a type of laser called the free-electron laser (FEL); these devices are called optical klystrons. Instead of microwave cavities, these use devices called undulators. The electron beam passes through an undulator, in which a laser light beam causes bunching of the electrons. Then the beam passes through a second undulator, in which the electron bunches cause oscillation to create a second, more powerful light beam.

Floating drift tube klystron

The floating drift tube klystron has a single cylindrical chamber containing an electrically isolated central tube. Electrically, this is similar to the two cavity oscillator klystron with considerable feedback between the two cavities. Electrons exiting the source cavity are velocity modulated by the electric field as they travel through the drift tube and emerge at the destination chamber in bunches, delivering power to the oscillation in the cavity. This type of oscillator klystron has an advantage over the two-cavity klystron on which it is based, in that it needs only one tuning element to effect changes in frequency. The drift tube is electrically insulated from the cavity walls, and DC bias is applied separately. The DC bias on the drift tube may be adjusted to alter the transit time through it, thus allowing some electronic tuning of the oscillating frequency. The amount of tuning in this manner is not large and is normally used for frequency modulation when transmitting.

Applications

Klystrons can produce far higher microwave power outputs than solid state microwave devices such as Gunn diodes. In modern systems, they are used from UHF (hundreds of megahertz) up to hundreds of gigahertz (as in the Extended Interaction Klystrons in the CloudSat satellite). Klystrons can be found at work in radar, satellite and wideband high-power communication (very common in television broadcasting and EHF satellite terminals), medicine (radiation oncology), and high-energy physics (particle accelerators and experimental reactors). At SLAC, for example, klystrons are routinely employed which have outputs in the range of 50 MW (pulse) and 50 kW (time-averaged) at 2856 MHz. The Arecibo Planetary Radar used two klystrons that provided a total power output of 1 MW (continuous) at 2380 MHz.

Popular Science's "Best of What's New 2007" described a company, Global Resource Corporation, currently defunct, using a klystron to convert the hydrocarbons in everyday materials, automotive waste, coal, oil shale, and oil sands into natural gas and diesel fuel.

Human givens

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Human_givens 

This is about psychotherapy. See Human condition for the general topic.

Human Givens is the name of a theory in psychotherapy formulated in the United Kingdom, first outlined by Joe Griffin and Ivan Tyrrell in the late 1990s. and amplified in the 2003 book Human Givens: A new approach to emotional health and clear thinking. The human givens organising ideas proffer a description of the nature of human beings, the 'givens' of human genetic heritage and what humans need in order to be happy and healthy. Human Givens therapy seeks to use a "client's strengths to enable them to get emotional needs met". It is advertised as "drawing from the best of person-centred counselling, motivational interviewing, cognitive behavioural therapy, psychoeducational approaches, interpersonal therapy, imaginal exposure and hypnotherapy". The Human Givens Institute has been accredited in the UK by the Professional Standards Authority for Health and Social Care (PSA).

Historical background

Abraham Maslow is credited with the first prominent theory which laid out a hierarchy of needs. The precise nature of the hierarchy and the needs have subsequently been refined by modern neuroscientific and psychological research.

Since Maslow's work in the middle of the twentieth century, a significant body of research has been undertaken to clarify what human beings need to be happy and healthy. The UK has contributed significantly to the international effort, through the ground breaking Whitehall Study led by Sir Michael Marmot, which tracked the lifestyles and outcomes for large groups of British civil servants. This identified effects on mental and physical health from emotional needs being met - for instance, it showed that those with less autonomy and control over their lives, or less social support, have worse health outcomes.

In the United States, the work of Martin Seligman, a psychologist at the University of Pennsylvania has been influential. Seligman has summarised the research to date in terms of what makes humans happy; again, this demonstrates themes about universal emotional needs which must be met for people to lead fulfilling lives.

At the University of Rochester, contemporaries of Seligman Edward Deci and Richard Ryan have conducted original research and gathered existing evidence to develop a framework of human needs which they call self-determination theory. This states that human beings are born with innate motivations, developed from our evolutionary past. They gather these motivational forces into three groups - autonomy, competence and relatedness. The human givens approach uses a framework of nine needs, which map onto these three groups.

Innate needs

The human givens model proposes that human beings come into the world with a given set of innate needs, together with innate resources to support them to get those needs met. Physical needs for nutritious food, clean water, air and sleep are obvious, and well understood, because when they are not met people die. However, the emotional needs, which the human givens approach seeks to bring to wider attention, are less obvious, and less well understood, but just as important to human health. Decades of social and health psychology research now support this.

The human givens approach defines nine emotional needs:

1. Security: A sense of safety and security; safe territory; an environment in which people can live without experiencing excessive fear so that they can develop healthily.
2. Autonomy and control: A sense of autonomy and control over what happens around and to us.
3. Status: A sense of status - being accepted and valued in the various social groups we belong to.
4. Privacy: Time and space enough to reflect on and consolidate our experiences.
5. Attention: Receiving attention from others, but also giving it; a form of essential nutrition that fuels the development of each individual, family and culture.
6. Connection to the wider community: Interaction with a larger group of people and a sense of being part of the group.
7. Intimacy: Emotional connection to other people - friendship, love, intimacy, fun.
8. Competence and achievement: A sense of our own competence and achievements, that we have what it takes to meet life's demands.
9. Meaning and purpose: Being stretched, aiming for meaningful goals, having a sense of a higher calling or serving others creates meaning and purpose.

These needs map more or less well to tendencies and motivations described by other psychological evidence, especially that compiled by Deci and Ryan at the University of Rochester. The exact categorisation of these needs, however, is not considered important. Needs can be interlinked and have fuzzy boundaries, as Maslow noted. What matters is a broad understanding of the scope and nature of human emotional needs and why they are so important to our physical and mental health. Humans are a physically vulnerable species that have enjoyed amazing evolutionary success due in large part to their ability to form relationships and communities. Getting the right social and emotional input from others was, in our evolutionary past, literally a matter of life or death. Thus, Human Givens theory states, people are genetically programmed only to be happy and healthy when these needs are met.

There is evidence that these needs are consistent across cultures, and therefore represent innate human requirements.

Innate resources

The Human Givens model also consists of a set of 'resources' (abilities and capabilities) that all human beings are born with, which are used to get the innate needs met. These constitute what is termed an 'inner guidance system'. Learning how to use these resources well is seen as being key to achieving, and sustaining, robust bio-psycho-social health as individuals and as groups (families, communities, societies, cultures etc.).

The given resources include:

• Memory: The ability to develop complex long-term memory, which enables people to add to their innate (instinctive) knowledge and learn;
• Rapport: The ability to build rapport, empathise and connect with others;
• Imagination: Which enables people to focus attention away from the emotions and problem solve more creatively and objectively (a 'reality simulator');
• Instincts and emotions: A set of basic responses and 'propulsion' for behaviours;
• A rational mind: A conscious, rational mind that can check out emotions, question, analyse and plan;
• A metaphorical mind: The ability to 'know', to understand the world unconsciously through metaphorical pattern matching ('this thing is like that thing');
• An observing self: That part of us which can step back, be more objective and recognise itself as a unique centre of awareness apart from intellect, emotion and conditioning;
• A dreaming brain: According to the expectation fulfilment theory of dreaming, this preserves the integrity of our genetic inheritance every night by metaphorically defusing emotionally arousing expectations not acted out during the previous day.

Three reasons for mental illness

A further organising idea proffered by the human givens approach is to suggest that there are three main reasons why individuals may not be getting their needs met and thus why they may become mentally ill:

1. Environment: something in our environment is interfering with our ability to get our needs met. Our environment is 'toxic' (e.g. a bullying boss, antisocial neighbours) or simply lacks what we need (e.g. community);
2. Damage: something is wrong with our 'resources' -- our 'hardware' (brain/body) or 'software' (missing or incomplete instincts and/or unhelpful conditioning such as posttraumatic stress disorder) is damaged;
3. Knowledge: we may not know what we need; or we may not have been taught, or may have failed to learn, the coping skills necessary for getting our needs met (for example, how to use the imagination for problem solving rather than worrying, or how to make and sustain friendships).

When dealing with mental illness or distress this framework provides a checklist that guides both diagnosis and treatment.

Key features

Key features of the human givens school include:

• A new model of therapeutic intervention (the APET model) based on the neurological finding that emotion precedes thought;
• New insights into trauma and how to treat it effectively - the 'rewind technique' (The human givens rewind technique has been evaluated in an international textbook on trauma.);
• An holistic understanding of the evolutionary origins and function of human dreaming (expectation fulfilment theory of dreaming) which is key to understanding the cycle of depression: how depression develops, is maintained and can be successfully treated;
• A neuroscience-based explanation for addiction and why withdrawal symptoms occur;
• A theory (called 'molar memories') which explains the mechanism that generates and maintains some instances of compulsive behaviour (such as sexual compulsions, anorexia and bulimia);
• A psychobiological explanation of clinical hypnosis, why it works and the mechanisms common to all forms of hypnotic induction;
• New understandings of the autistic spectrum disorder, including what has been termed ‘caetextia’;
• New insights into the nature of psychosis (waking reality processed through the REM state/dreaming brain);
• A clear protocol for conducting therapy sessions - the RIGAAR model: Rapport building; Information gathering; Goal setting (new, positive expectations related to the fulfillment of innate needs); Accessing the client's own strengths and resources (success templates); Agreeing a strategy (for achieving the needs-related goals); Rehearsing success (the enactment of the agreed strategies).

Research and evidence

There are now a number of independent studies evaluating the human givens approach:

• Human givens randomised controlled trial: There are no randomised-controlled trials (RCTs) to test the human givens approach. The first RCT is in process; The Bristol Randomised Controlled Trial Collaboration (a partnership between the University of Bristol and the National Health Service) has agreed to help design it.
• A 12–month evaluation of the human givens approach in primary care (2011): Peer reviewed evidence for the effectiveness of human givens therapy, published in Psychology and Psychotherapy: Theory, Research and Practice, showed that, of 120 patients treated by HG therapists in a GP's surgery, more than three-quarters were either symptom-free or reliably improved as a result of the therapy. This was accomplished in an average of only 3.6 sessions. This compares favourably with the recovery rate for the UK Government’s Improving Access to Psychological Therapies (IAPT) programme, which mainly uses therapists trained in cognitive-behavioural therapy (CBT) and expects therapy to take longer; less than half of its patients improve or recover.
• Using human givens therapy to support the wellbeing of adolescents (2011): An article for Pastoral Care in Education: An International Journal of Personal, Social and Emotional Development assessed the efficacy of an individual human givens intervention for three young people who reported high anxiety or depression and/or low self-concept. It found positive outcomes for the subjects which provided tentative evidence that human givens therapy might be useful to practitioners delivering therapeutic interventions in schools.
• Assessing the effectiveness of the “human givens” approach in treating depression (2012): A peer-reviewed research paper, published in Mental Health Review Journal found that treating people with mild to moderate depressed mood (measured using HADS) with human givens therapy had quicker results than the treatment provided to people in a control group.
• The Emotional Needs Audit: a report on its reliability and validity (2012): A peer-reviewed research paper published in the Mental Health Review Journal found that the Human Givens Institute’s Emotional Needs Audit (ENA) was a valid and reliable instrument for measuring wellbeing, quality of life and emotional distress. It also concluded that the ENA allows insight into the causes of symptoms, dissatisfaction and distress, complementing standardised tools when used in clinical practice.
• A 5–year evaluation of the human givens therapy using a Practice Research Network (2012): A peer-reviewed research paper published in the Mental Health Review Journal (2012) evaluated five year’s worth of practice-based evidence gleaned from a practice research network. The pre-post treatment effect size suggested that “clients treated using the HG approach experienced relief from psychological distress”.
• Evaluation of human givens ‘rewind’ treatment to treat trauma (2013): A poster presentation for a veteran lead research conference evaluated the effectiveness of a single human givens rewind treatment session to treat PTSD in the general psychiatric population and found that this treatment can be effective with severe, chronic and even multiple traumas in a single session, with some requiring no further treatment.

Organisations

The following constitute the main human givens organisations:

Human Givens Institute

The Human Givens Institute is a membership organisation open to those wishing to support and promote the human givens approach through all forms of psychological, educational and social interactions, and the professional body representing the interests of those in the caring and teaching professions who aim to work in alignment with the best scientific knowledge available about the givens of human nature. The Institute is accredited by the Professional Standards Authority for Health and Social Care. for the purposes of regulating practitioners who have completed training as Human Givens Therapists and who are Registered with the Institute.

Human Givens Foundation

The Human Givens Foundation is a charitable organisation devoted to spreading the human givens philosophy and information into organisations concerned with health, education, business, social work and the wider care system, the police, the armed forces, and, more widely, into social policy and government. It aims to support parents, families, couples and individuals to live more harmonious, satisfying and meaningful lives.

Human Givens College

Human Givens College is a training organisation offering psychotherapy courses as well as a full psychotherapy diploma course leading to qualification as a human givens practitioner. There are currently 226 Registered Members on the HGI Register – people who have achieved part 3 of the diploma course and are set up in private practice.

Ecological fallacy

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Ecological_fallacy

 

An ecological fallacy (also ecological inference fallacy or population fallacy) is a formal fallacy in the interpretation of statistical data that occurs when inferences about the nature of individuals are deduced from inferences about the group to which those individuals belong. 'Ecological fallacy' is a term that is sometimes used to describe the fallacy of division, which is not a statistical fallacy. The four common statistical ecological fallacies are: confusion between ecological correlations and individual correlations, confusion between group average and total average, Simpson's paradox, and confusion between higher average and higher likelihood.

Examples

Mean and median

An example of ecological fallacy is the assumption that a population mean has a simple interpretation when considering likelihoods for an individual.

For instance, if the mean score of a group is larger than zero, this does not imply that a random individual of that group is more likely to have a positive score than a negative one (as long as there are more negative scores than positive scores an individual is more likely to have a negative score). Similarly, if a particular group of people is measured to have a lower mean IQ than the general population, it is an error to conclude that a randomly-selected member of the group is more likely than not to have a lower IQ than the mean IQ of the general population; it is also not necessarily the case that a randomly selected member of the group is more likely than not to have a lower IQ than a randomly-selected member of the general population. Mathematically, this comes from the fact that a distribution can have a positive mean but a negative median. This property is linked to the skewness of the distribution.

Consider the following numerical example:

• Group A: 80% of people got 40 points and 20% of them got 95 points. The mean score is 51 points.
• Group B: 50% of people got 45 points and 50% got 55 points. The mean score is 50 points.
• If we pick two people at random from A and B, there are 4 possible outcomes:
  • A – 40, B – 45 (B wins, 40% probability – 0.8 × 0.5)
  • A – 40, B – 55 (B wins, 40% probability – 0.8 × 0.5)
  • A – 95, B – 45 (A wins, 10% probability – 0.2 × 0.5)
  • A – 95, B – 55 (A wins, 10% probability – 0.2 × 0.5)
• Although Group A has a higher mean score, 80% of the time a random individual of A will score lower than a random individual of B.

Individual and aggregate correlations

Research dating back to Émile Durkheim suggests that predominantly Protestant localities have higher suicide rates than predominantly Catholic localities. According to Freedman, the idea that Durkheim's findings link, at an individual level, a person's religion to his or her suicide risk is an example of the ecological fallacy. A group-level relationship does not automatically characterize the relationship at the level of the individual.

Similarly, even if at the individual level, wealth is positively correlated to tendency to vote Republican, we observe that wealthier states tend to vote Democratic. For example, in 2004, the Republican candidate, George W. Bush, won the fifteen poorest states, and the Democratic candidate, John Kerry, won 9 of the 11 wealthiest states. Yet 62% of voters with annual incomes over $200,000 voted for Bush, but only 36% of voters with annual incomes of $15,000 or less voted for Bush. Aggregate-level correlation will differ from individual-level correlation if voting preferences are affected by the total wealth of the state even after controlling for individual wealth. It could be that the true driving factor in voting preference is self-perceived relative wealth; perhaps those who see themselves as better off than their neighbours are more likely to vote Republican. In this case, an individual would be more likely to vote Republican if she became wealthier, but she would be more likely to vote for a Democrat if her neighbor's wealth increased (resulting in a wealthier state).

However, the observed difference in voting habits based on state-level and individual-level wealth could also be explained by the common confusion between higher averages and higher likelihoods as discussed above. States may not be wealthier because they contain more wealthy people (i.e. more people with annual incomes over $200,000), but rather because they contain a small number of super-rich individuals; the ecological fallacy then results from incorrectly assuming that individuals in wealthier states are more likely to be wealthy.

Many examples of ecological fallacies can be found in studies of social networks, which often combine analysis and implications from different levels. This has been illustrated in an academic paper on networks of farmers in Sumatra.

Robinson's paradox

A 1950 paper by William S. Robinson computed the illiteracy rate and the proportion of the population born outside the US for each state and for the District of Columbia, as of the 1930 census. He showed that these two figures were associated with a negative correlation of −0.53; in other words, the greater the proportion of immigrants in a state, the lower its average illiteracy. However, when individuals are considered, the correlation was +0.12 (immigrants were on average more illiterate than native citizens). Robinson showed that the negative correlation at the level of state populations was because immigrants tended to settle in states where the native population was more literate. He cautioned against deducing conclusions about individuals on the basis of population-level, or "ecological" data. In 2011, it was found that Robinson's calculations of the ecological correlations are based on the wrong state level data. The correlation of −0.53 mentioned above is in fact −0.46. Robinson's paper was seminal, but the term 'ecological fallacy' was not coined until 1958 by Selvin.

Formal problem

The correlation of aggregate quantities (or ecological correlation) is not equal to the correlation of individual quantities. Denote by X_i, Y_i two quantities at the individual level. The formula for the covariance of the aggregate quantities in groups of size N is

${\displaystyle \operatorname {cov} \left(\sum _{i=1}^{N}Y_{i},\sum _{i=1}^{N}X_{i}\right)=\sum _{i=1}^{N}\operatorname {cov} (Y_{i},X_{i})+\sum _{i=1}^{N}\sum _{l\neq i}\operatorname {cov} (Y_{l},X_{i})}$

The covariance of two aggregated variables depends not only on the covariance of two variables within the same individuals but also on covariances of the variables between different individuals. In other words, correlation of aggregate variables take into account cross sectional effects which are not relevant at the individual level.

The problem for correlations entails naturally a problem for regressions on aggregate variables: the correlation fallacy is therefore an important issue for a researcher who wants to measure causal impacts. Start with a regression model where the outcome ${\displaystyle Y_{i}}$ is impacted by ${\displaystyle X_{i}}$

${\displaystyle Y_{i}=\alpha +\beta X_{i}+u_{i},}$

${\displaystyle \operatorname {cov} [u_{i},X_{i}]=0.}$

The regression model at the aggregate level is obtained by summing the individual equations:

${\displaystyle \sum _{i=1}^{N}Y_{i}=\alpha \cdot N+\beta \sum _{i=1}^{N}X_{i}+\sum _{i=1}^{N}u_{i},}$

${\displaystyle \operatorname {cov} \left[\sum _{i=1}^{N}u_{i},\sum _{i=1}^{N}X_{i}\right]\neq 0.}$

Nothing prevents the regressors and the errors from being correlated at the aggregate level. Therefore, generally, running a regression on aggregate data does not estimate the same model than running a regression with individual data.

The aggregate model is correct if and only if

${\displaystyle \operatorname {cov} \left[u_{i},\sum _{k=1}^{N}X_{k}\right]=0\quad {\text{ for all }}i.}$

This means that, controlling for ${\displaystyle X_{i}}$, ${\displaystyle \sum _{k=1}^{N}X_{k}}$ does not determine ${\displaystyle Y_{i}}$.

Choosing between aggregate and individual inference

There is nothing wrong in running regressions on aggregate data if one is interested in the aggregate model. For instance, for the governor of a state, it is correct to run regressions between police force on crime rate at the state level if one is interested in the policy implication of a rise in police force. However, an ecological fallacy would happen if a city council deduces the impact of an increase in police force in the crime rate at the city level from the correlation at the state level.

Choosing to run aggregate or individual regressions to understand aggregate impacts on some policy depends on the following trade-off: aggregate regressions lose individual level data but individual regressions add strong modeling assumptions. Some researchers suggest that the ecological correlation gives a better picture of the outcome of public policy actions, thus they recommend the ecological correlation over the individual level correlation for this purpose (Lubinski & Humphreys, 1996). Other researchers disagree, especially when the relationships among the levels are not clearly modeled. To prevent ecological fallacy, researchers with no individual data can model first what is occurring at the individual level, then model how the individual and group levels are related, and finally examine whether anything occurring at the group level adds to the understanding of the relationship. For instance, in evaluating the impact of state policies, it is helpful to know that policy impacts vary less among the states than do the policies themselves, suggesting that the policy differences are not well translated into results, despite high ecological correlations (Rose, 1973).

Group and total averages

Ecological fallacy can also refer to the following fallacy: the average for a group is approximated by the average in the total population divided by the group size. Suppose one knows the number of Protestants and the suicide rate in the USA, but one does not have data linking religion and suicide at the individual level. If one is interested in the suicide rate of Protestants, it is a mistake to estimate it by the total suicide rate divided by the number of Protestants. Formally, denote ${\displaystyle P[{\text{Suicide}}\mid {\text{Protestant}}]}$ the mean of the group, we generally have:

${\displaystyle P[{\text{Suicide}}\mid {\text{Protestant}}]\neq {\frac {P[{\text{Suicide}}]}{P({\text{Protestant}})}}}$

However, the law of total probability gives

${\displaystyle {\begin{aligned}P[{\text{Suicide}}]={\color {Blue}P[{\text{Suicide}}\mid {\text{Protestant}}]}P({\text{Protestant}})+{\color {Blue}P[{\text{Suicide}}\mid {\text{not Protestant}}]}(1-P({\text{Protestant}}))\end{aligned}}}$

As we know that ${\displaystyle P[{\text{Suicide}}\mid {\text{not Protestant}}]}$ is between 0 and 1, this equation gives a bound for ${\displaystyle P[{\text{Suicide}}\mid {\text{Protestant}}]}$.

Simpson's paradox

Main article: Simpson's paradox

A striking ecological fallacy is Simpson's paradox: the fact that when comparing two populations divided into groups, the average of some variable in the first population can be higher in every group and yet lower in the total population. Formally, when each value of Z refers to a different group and X refers to some treatment, it can happen that

${\displaystyle E[Y\mid Z=z,X=1]>E[Y\mid Z=z,X=0]\ {\text{for all }}z,{\text{ while }}E[Y\mid X=1]<E[Y\mid X=0]}$

When ${\displaystyle E[Y\mid Z=z,X=1]-E[Y\mid Z=z,X=0]}$ does not depend on ${\displaystyle Z}$, the Simpson's paradox is exactly the omitted variable bias for the regression of Y on X where the regressor ${\displaystyle X}$ is a dummy variable and the omitted variable ${\displaystyle Z}$ is a categorical variable defining groups for each value it takes. The application is striking because the bias is high enough that parameters have opposite signs.

Legal applications

The ecological fallacy was discussed in a court challenge to the 2004 Washington gubernatorial election in which a number of illegal voters were identified, after the election; their votes were unknown, because the vote was by secret ballot. The challengers argued that illegal votes cast in the election would have followed the voting patterns of the precincts in which they had been cast, and thus adjustments should be made accordingly. An expert witness said this approach was like trying to figure out Ichiro Suzuki's batting average by looking at the batting average of the entire Seattle Mariners team, since the illegal votes were cast by an unrepresentative sample of each precinct's voters, and might be as different from the average voter in the precinct as Ichiro was from the rest of his team. The judge determined that the challengers' argument was an ecological fallacy and rejected it.