NANOTECHNOLOGY

Nanotechnology is application of novel behaviour that occurs at the nano-scale to solve real-life problems. This discipline requires a breadth of understanding that is much wider than just the equations and scientific principles that underlie that behaviour. This introductory module will give an overview of the current state of the technology as well as sketching out the implications of these new technologies for safety, regulation, innovation and will give an overview of the societal and environmental implications.
www.cpd.conted.ox.ac.uk

Goods have no natural meaning, their meaning is the result of sociocultural construc-tion and interpretation. To determine what is a just distribution of the good we have to determine what it means to those for whom it is a good. In the medical, the politi-cal, and the commercial spheres there are different goods — medical treatment, po-litical office, and money — which are allocated by means of different allocation or distributive practices: medical treatment on the basis of need, political office on the basis of desert, and money on the basis of free exchange. What ought to be prevented, and often is prevented as a matter of fact, is the dominance of particular goods. A good is called dominant if the individuals that have it, because they have it, can com-mand a wide range of other goods.
Van Den Hoven et al, Nano-Technology and Privacy: On Continuous Surveillance Outside the Panopticon; http://jmp.oxfordjournals.org




For want of a nail, the shoe was lost;
For want of a shoe, the horse was lost;
For want of a horse, the rider was lost;
For want of a rider, a message was lost;
For want of a message the battle was lost;
For want of a battle, the kingdom was lost!

Small variations in initial conditions result in huge, dynamic transformations in concluding events.




Looking Beyond the Instruments

New opinions are always suspected, and usually opposed, without any other reason but because they are not already common. -John Locke, Essay on Human Understanding




Technology to some extent is the essence of life of social human beings, the essence of human nature combined with dynamic thoughts and movements. It is the basic theory against which we measure or compare thoughts, ideas and movements. 'Teche' in ancient Greece was synonymous with poeisis, implying to significant role of technology in inspiring and in moving societies. In this sense poetry and technology were equally playing part in meaning making, in creating culture and materials, but also in connecting societies that would contribute to economies. Historically, advances in our understanding of material process have exceeded advances in our understanding of social processes. As a result, vast social potential has been created, but men and women in societies have not yet acquired the capacity to advance their mental engagements at the same pace.

Wireless technologies and computer chips are just a few of the current technologies influencing the urban environment while they are expected to extend the connection to all corners. How cities will be developed and where growth will occur will be defined by the technologies of the future as well as our intellectual capacity for creative usage. It is with the new technology that lies potential advancement and empowerment with which societies thrive.

Goods have no natural meaning, their meaning is the result of sociocultural construction and interpretation. Technologies have created new cultural contexts for understanding social interactions, for players as well as for objects. The technological texts are symbols for group connectedness, and other ways of writing and reading. Decoding categorical paradigms such as body, mind and machine allows us to refashion social categories and hierarchies. There is powerful divisional dimension to the process of analysing data and information which needs to be included in decision making process. Our cognitive processes are measured by technology and shaped by technology which mediates our relationships with objects of the material and physical world.

Initially men sailing through the world of technology forged instruments that were perceived as traditionally ordinary and managed to have freshen them up, producing contemporary function and image. An object made of a component draws the fact as to how groups see materials differently: either for their functionality or aesthetic stimulation, or simply unfamiliarity. Whether material is used and viewed for beautiful reflection of the light or to improve resistance to rusting, is the matter of choice.

The question is how different we see materials in the way we perceive aesthetics, arts, language, communication, culture and relationships? how differently critiques take position in our relations with materials? The way we react to materials influence manufacturers and intrigue the rethinking force behind social categories and hierarchies. As we move further, technology imitates material. When plastics first came on the market people were uneasy with the new material but when it was shaped like something familiar to use and were affordable, men and women made use of them in different ways. Environment and space affect us in a similar way. Just as caring for the environment has to maintain a balancing act between many things since some has bigger impact than others.

Designers of the Jaguar car since 1940 have used different techniques in improving the image that is associated in popular culture with fame and fortune. And to this end are targeting light metals that are often used to reduce the weight of components and structures. Strength to weight ratios together with stillness and resistance to buckling are the focus in this enterprise, where sheet has to meet demanding requirements such as formability and the minimum gauge to provide the maximum weight.

Elsewhere, in '1995' the Carbon Fibre reinforced composite of the high strength Kayak that weight only 6 kg was used by Lynn Simpson when she won the Gold Medal for Britain in the world Slalom Championship.

Jaguar has gone under further improvement. The super efficient Hi-tech and highly sensitive injectors made of material called peizoelectric polymers have managed to over come many problems of the previous engine. This urge for improvement and growth is an endowment of human beings, living organisms compelled to develop by a pressure within themselves, which in turn gives life and energy to the growth of the instruments and systems they create. The theory has to outline enabling space and describe rules and regulations to allow growth and development to be placed at the centre.

Social behaviours, skills, attitudes, customs, traditions, systems, formal organizations, non-formal institutions, cultural values; and technical language, data, facts, information, beliefs, opinions, systems of thought, ideas, theories, and spiritual values-all of which interact and influence each other to impact the course of human development. The advancement of diverse groups as a condition to the new social order is expected to be engineered by people from all divisions and should not be seen in isolation for any group issue. Technology Regime and Mind-set is based on democratic use of instruments, being the only way to build a sustainable, just and developed society.

A theory of development should aim at a knowledge that will enable society from multi dimensional aspects to more consciously and effectively put in practice its development potentials utilizing new instruments productively. The first challenge is to select the right materials for the job. The priority is to match the properties of the materials to the task to be performed.

Strategic implications of a wide range of global trends such as the new economy, the digital society, financial services, biotechnology, health care, lifestyle changes, consumer behaviour, public policy, corporate ethics, and social responsibility needs the engineering of a new social development paradigm. The purpose is to develop and share a common framework composed of easily understood, scientifically based principles that can serve as a basis to move society toward sustainability.



References:


- The British Museum of Science and Society, www.sciencemuseum.org.uk

- Royal Academy of Arts, London, Luxury in Living, Italian Design Exhibition, www.luxuryinliving.com

- The Urban Land Institute: http://www.uli.org/AM/Template.cfm

- Champion A, Flight From the Cities, Home Alone; School of Geography, Politics, and Sociology University of Newcastle

- Dixon P, Futurewise: Six Faces of Global Change; Global Change Ltd. London

- Jennifer James, Thinking in the Future Tense; Urban/Cultural Anthropologist, Jennifer James Inc

- Textuality — an open, infinite process that is meaning-generating and subverting.
http://www.electronicbookreview.com/v3/servlet/ebr?essay_id=seamanr2&command=view_essay

- www.oxfordtoday.ox.ac.uk- Ageing Society, Vol 16, No 2, 2

- The Oxford Times, May 25, www.theoxfordtimes.net/display.var.1424224.0.0.php

- Bandura, Social foundations of thought and action: A social cognitive theory. Englewood Cliffs, NJ: Prentice Hall, 1986

- Colcombe. S.J. et al. Medical. Science 61,1166 - 1170, 2006

- Gosden, C., Social Being and Time, Blackwell Publishers, 1994

- Van Den Hoven et al, Nano-Technology and Privacy: On Continuous
Surveillance Outside the Panopticon; http://jmp.oxfordjournals.org

- Snow D, White C, Morril C; Together Alone, Personal Relationships in Public Places, Univ of California Press, 2005

- World Bank; Health Systems Development, June 2005; www.worldbank.org

google advice

Oxfordshire by-election

John Howell explains “It is a huge privilege to have been selected as the Conservative candidate for my home constituency. I plan to spend the next few weeks talking to as many local people as possible about the issues that affect us all in South Oxfordshire.

"Boris has been a great MP for this area and he will be a hard act to follow for the next person who represents the Henley constituency. I'm looking forward to the next three weeks of campaigning until 26 June - it is an opportunity to show people that I will be their local champion.

“I have lived here for twenty years, so I know the area well. And I always stand up for the community - I have campaigned to protect local services and prevented Green Belt development. This by-election is also a chance to keep the pressure on Gordon Brown after his disastrous first year in charge. That's what I will do if people choose me on 26 June."

http://www.henleyconservatives.com/

Dementia risk factors

Dementia risk factors

...Relative to nonsmoking, current smoking, past smoking, and pack-years were not significantly related to change in immediate memory. None was significantly related to change in orientation. Only pack-years was significantly related to normal change score in digit span (normal change score change per unit of predictor=0.001, 95% confidence interval 0.0003–0.002).
American Journal of Epidemiology Vol. 137, No. 8: 881-891, Oxford Journals


.....Alcohol and smoking (never, past and current) were neither strongly protective nor predictive. Poor self-perceived health (versus good) increased the risk for incident dementia (OR = 3.9, 95% CI = 2.2–6.9).

Risk factors for incident dementia in England and Wales: Oxford Journals



.........The authors assessed the association of smoking with dementia and cognitive decline in a meta-analysis of 19 prospective studies with at least 12 months of follow-up. Studies included a total of 26,374 participants followed for dementia for 2–30 years and 17,023 participants followed up for 2–7 years to assess cognitive decline. Mean study age was 74 years. Current smokers at baseline, relative to never smokers, had risks of 1.79 (95% confidence interval (CI): 1.43, 2.23) for incident Alzheimer's disease, 1.78 (95% CI: 1.28, 2.47) for incident vascular dementia, and 1.27 (95% CI: 1.02, 1.60) for any dementia.

A Meta-Analysis of Prospective Studies: American Journal of Epidemiology Advance Access originally published online on June 14, 2007; Oxford Journals




........Less educated patients became demented later and died later, but cognitive function declined at the same rate in all educational groups and there was no difference in the burden of neurodegenerative lesions between them. However, the less educated patients had more cerebrovascular lesions. It can be concluded that higher education does not modify the course of Alzheimer's disease, but lower education relates to the occurrence of cerebral infarcts. Our results suggest that a `brain battering' model related to the higher prevalence of small vascular lesions in less educated individuals may explain their increased risk of dementia described by epidemiological studies better than the prevalent `brain reserve' hypothesis.

An autopsy-verified study of the effect of education on degenerative dementia; Brain, Vol. 122, No. 12, 2309-2319, December 1999; OUP



........However, the basis for the relationship between low educational attainment and cognitive decline or poor performance on cognitive tests is not so clear. Underlying mechanisms have been proposed based on the functional brain reserve hypothesis. Yet it is widely accepted that lower levels of education are associated with diminished performance on tests of cognitive ability. This is a particularly relevant issue for studies with US immigrants, where low levels of formal education are highly prevalent and where cognitive assessment is usually done with instruments developed for populations with different education levels and culture. One study (2000) found that performance in normal individuals with no schooling was as low as that of subjects with severe dementia, whereas the score for those with 1 to 4 years of schooling was similar to that of subjects with slight dementia.

...............Most of the instruments used in survey studies have conventional cut-off scores originally used in their norming sample study or adapted for the purpose of each survey, but neither one considers different cut-off scores for the different educational levels. Cognitive impairment may be overestimated in Spanish-speaking subjects when conventional cut-off scores are used. Recently,we have found that the Mini-mental State Examination (MMSE) cut-off point of 23 or 24 in Mexicans with 5 years or less of formal education results in very low specificity values (23% to 28%), which means that a large amount of normal subjects with low educational level will be erroneously classified as cognitively impaired. This finding is in agreement with Gurland (1992), who suggested that conventional scores produce an increase in false positives for minority groups, especially Hispanics. Poor performance in Spanish-speaking populations has been attributed to low schooling and ethnic and cultural differences. One method aimed to identify subjects with cognitive impairment considering the effect of confounding variables such as education, is the use of percentile distribution obtained by ranking the data values in ascending order from lowest to highest score within each educational level. The percentile technique is appropriate for data with non-Gaussian distributions and is
commonly used to rank candidates in an examination. It provides an approach that can be used to evaluate individual subjects against the distribution of scores in a particular population.....

Comparative Analysis of Cognitive Impairment Among... Immigrant’s Elders;
http://jah.sagepub.com/cgi/reprint/18/2/292



According to widely circulated global burden estimates, unipolar depressive disorders are the leading cause of disability adjusted life-years (DALYs) in the Americas and the third leading cause in Europe. …Individuals living with others with poor mental health are also significantly more likely to report worse mental health themselves. In contrast, there is little observed relationship between mental health and poverty or education, common measures of socio-economic status. The results instead suggest that economic and multi-dimensional shocks such as illness or crisis can have a greater impact on mental health than overall levels of poverty. This may have important implications for social protection policy. The authors also find significant associations between poor mental health and lowered labour force participation (especially for women) and higher frequency visits to health centres, suggesting that poor mental health can have significant economic consequences for households and the health system. Finally, the paper discusses how measures of mental health are distinct from general subjective welfare measures such as happiness and indicate useful directions of future research.
…. However, it is also plausible that the relationship could be causal, whereby the presence of one household member with poor mental health creates a poor mental health environment for other household members, i.e. a “contagion” effect. Tables 2 and 3 show that there is indeed a strong and significant positive relationship between an individual’s mental health and that of his or her family.10 A one standard deviation change in the mental health of household members is associated with a 0.22 to 0.59 standard deviation change in own mental health.

….. There is evidence in some countries that lower mental health is associated with reduced labour force participation, especially for women. Mental health is also a significant predictor of health care utilization and thus perhaps burdens a health system ill-equipped to diagnose and provide care.
Mental Health Patterns and Consequences, Policy Research Working Paper 4495, The World Bank

- The association found between mental disability and Education may be explained by more logical approach to life events. Rather than years of education, the focus should be on taking account of emotional capacity in dementia and AD.
- Education years is not a satisfactory indicator, the trends for continuous mental ac-tivity need to be accounted for, to provide better example of the state of mind at the time of disease development.
- Protective factors in terms of healthy diet studies are so inadequate in their assess-ment and data to infer reliable conclusion, caused mostly due to inattention to take accurate account of food intake habits, and trends. This is particularly true for rare incidence of Alzheimer and dementia, which needs more thorough study particularly on those who did develop the disease. Who on the earth would measure daily intake of their fruit consumption, I wonder ?? the studies only find relevance where national eating habits are brought into account versus the regional prevalence of dementia.(me)

...........However, statistical significance says little about the magnitude or precision of an estimated association, and is especially misleading when its absence is misinterpreted as absence of an association. Absence of significance signifies only that the association was estimated too imprecisely to determine the direction with confidence, and often reflects more the limited size of the sample than the size of the association.
http://ije.oxfordjournals.org/cgi/content/full/32/4/553




OXFORD PROJECT TO EXAMINE MEMORY AND AGEING

The challenge
• Each year about 203,000 people in the UK develop dementia (550 every day), the great majority with Alzheimer’s disease.
• Alzheimer’s disease costs the country about £17 billion per year, which is almost 20% of the health budget. The costs of Alzheimer’s disease are more than the combined costs of heart disease, stroke and cancer.
• The main challenge is to discover ways of preventing Alzheimer’s disease from developing.


How is OPTIMA dealing with the challenge?

1. In 1992, OPTIMA introduced new methods of diagnosis of Alzheimer’s disease, in use around the world.

2. In 1994 OPTIMA discovered that Alzheimer’s disease is not an inevitable part of ageing, but that it is a true disease. This finding led OPTIMA to search for ‘risk factors’.

3. In 1998, OPTIMA discovered the first risk factor for Alzheimer’s disease that can be safely and simply modified by diet (homocysteine. This discovery was recognised by the American Medical Association as one of the most significant findings of the year. OPTIMA’s discovery has been confirmed world-wide and has led the US National Institute on Aging to set up a clinical trial in which B vitamins, which lower homocysteine levels, are being tested to see if they can slow the progression of Alzheimer’s disease.

http://www.medsci.ox.ac.uk/optima



Folate, Vitamin B12, and Serum Total Homocysteine Levels in Confirmed Alzheimer Disease

Recent studies suggest that vascular disease may contribute to the cause of Alzheimer disease (AD). Since elevated plasma total homocysteine (tHcy) level is a risk factor for vascular disease, it may also be relevant to AD.

Low blood levels of folate and vitamin B12, and elevated tHcy levels were associated with AD. The stability of tHcy levels over time and lack of relationship with duration of symptoms argue against these findings being a consequence of disease and warrant further studies to assess the clinical relevance of these associations for AD.

Serum tHcy levels were significantly higher and serum folate and vitamin B12 levels were lower in patients with DAT and patients with histologically confirmed AD than in controls. The odds ratio of confirmed AD associated with a tHcy level in the top third (>=14 µmol/L) compared with the bottom third (<=11 µmol/L) of the control distribution was 4.5 (95% confidence interval, 2.2-9.2), after adjustment for age, sex, social class, cigarette smoking, and apolipoprotein E {epsilon}4. The corresponding odds ratio for the lower third compared with the upper third of serum folate distribution was 3.3 (95% confidence interval, 1.8-6.3) and of vitamin B12 distribution was 4.3 (95% confidence interval, 2.1-8.8). The mean tHcy levels were unaltered by duration of symptoms before enrollment and were stable for several years afterward. In a 3-year follow-up of patients with DAT, radiological evidence of disease progression was greater among those with higher tHcy levels at entry.


http://archneur.ama-assn.org/cgi/content/full/55/11/1449



As researchers learn more about FTLD through MRI scans of patients' brains, Levenson said they will be better able to pinpoint the brain circuits responsible for certain emotions and promote awareness of what is a devastating and still misunderstood disease. Levenson said. "If you understand that emotional response changes result from a brain disease, you are likely to have a different reaction and be more supportive."

Levenson and Miller published an overview of their findings in the December 2007 issue of the journal Current Directions in Psychological Science after conducting intensive laboratory studies of FTLD patients that included brain scans, precise tests of emotional functioning, and interviews. While study participants reacted normally to very simple emotional stimuli, they lacked complex emotions such as embarrassment or compassion, and they had difficulty recognizing emotions in others.

"Embarrassment is an emotion that lets us know we have violated social norms and motivates us to take corrective actions. Without emotions such as embarrassment, we behave very inappropriately in social situations," Levenson said.

Compared to Alzheimer's disease, which is marked by dramatic memory loss and typically occurs in old age, frontotemporal dementia usually shows up before age 65 and is commonly mistaken for depression and other psychiatric disorders. At present, there is no effective treatment for FTLD.

FTLD affects as many as 15 percent of dementia sufferers, according to Levenson. The average time from diagnosis to death is five years. While it is unknown at what age FTLD actually begins, the symptoms usually appear in a person's 50s. Triggering the death of brain cells are proteins, such as tau, that accumulate in the neurons of the central nervous system. They particularly build up in the frontal and temporal lobes and literally smother the brain cells to death.

http://www.physorg.com/news127573514.html

50 Million Gift to Christ Church

Michael Moritz and Harriet Heyman have donated $50m (over £25m) to Christ Church, Oxford. Under the terms of the gift, Christ Church will transfer an additional £75m of its existing endowment into the Oxford University Asset Management fund, which was established recently to improve the management of the University’s long-term funds. Christ Church’s total stake in the University’s investment pool will rise to over £100m.

www.ox.ac.uk

Loss of Insight in AD

Apathy was significantly correlated with decreased right temporoparietal perfusion and problem behaviors. Loss of insight was significantly correlated with decreased right temporo-occipital perfusion and impairment in daily functioning. Dementia severity as measured by the Mini-Mental State Examination (MMSE) was a poor predictor of behavioral problems or daily functioning. These data suggest that global measures of cognitive ability, which are weighted toward measuring left hemisphere function, are less important as indicators of management problems in AD than are measures of right hemisphere function such as motivation and insight.

J Neuropsychiatry Clin Neurosci 1996; 8:41-46
BR Ott, RB Noto and BS Fogel
Roger Williams Medical Center Division of Neurology, Providence, RI 02908, US
http://neuro.psychiatryonline.org/cgi/content/abstract/8/1/41

Evidence and The Process of Reasoning

Cigarette, Cancer and Statistics

Sir Ronal Fisher, 1958

...I have been concerned with the problem of how experimentation should be carried out, how reasoning processes should be applied to the data supplied by experimentation or by survey so as to give really conclusive answers.

.....So our evidence about inhaling is embarrasing and difficult. There is no doubt that inhaling is more common among heavy cigarette smokers than among light cigarette smokers in Great Britain, where inhaling isnot nearly a universal practice. There is no doubt that cancer is commoner among the heavy cigarette smokers than among the light cigarette smokers. Consequently, if inhaling had no effect whatever, you would expect to find more inhalers among the cancer patients than among the non-cancer patients. There would be an indirect correlation through the association of both with the quantity smoked. Now, of course, in what was reported everything was thrown together; and yet, in the aggregate data, it appeared that the cancer patients had the fewer inhalers than the non-cancer patients. It would look as though, if one could make the inquiry by comparing people who smoke the same number of cigarettes, there would be a negative association between cancer and inhaling. It seems to me the world ought to know the answer to that question. Before I stop, in fact, I hope I shall make clear that there is a case for further research, and I shall only mention two areas which would seem to be profitable for investigation. I would stress the importance of what could be done comparatively easily with rather little expense, namely, to ascertain unmistakably what the facts are about inhaling. If inhaling is found to be strongly associated with lung cancer, it would be consonant with the view that the products of combustion, wafted over the surface of the bronchus, might induce a precancerous and thence a cancerous condition. But if there is either no association at all or a negative association, we should have to reject altogether that simple theory of the causation of cancer.

The subject is complicated, and I mentioned at an early stage that the logical distinction was between A causing B, B casing A, something else causing both. Is it possible, then, that lung cancer – that is to say, the precancerous condition which must exist and is known to exist for years in those who are going to show overt lung cancer – is one of the causes of smoking cigarettes? I don’t think it can be excluded. I don’t think we know enough to say that it is such a cause. But the precancerous condition is one involving a certain amount of slight chronic inflammation. The causes of smoking cigarettes may be studied among your friends. To some extent, and I think you will agree that a slight cause of irritation – a lsight disappointment, an unexpected delay, some sort of a mild rebuff, a frustration- are commonly accompanied by pulling out a cigarette and getting a little compensation for life’s minor ills in that way. And so, anyone suffering from a chronic inflammation in part of the body (something that does not give rise to conscious pain) is not unlikely to be associated with smoking more frequently, or smoking rather than not smoking. It is the kind of comfort that might be a real solace to anyone in the fifteen years of approaching lung cancer. And to take the poor chap’s cigarettes away from him would be rather like taking away his white stick from a blind man. It would make an already unhappy person a little more unhappy than he need be.

...There is the attitude of a man (may I say, I think it is an entirely rational attitude and one within his own competence to judge) who says, 'There seems to be some danger - I cant assess whether it is infinitesimal or serious. This habit of mine of smoking isnt very important to me. I will give up smoking as a kind of insurance against a danger which I am quite unable to assess.' That seems to me a perfectly rational attitude. What is not quite so much the work of a good citizen is to plant fear in the minds of perhaps a hundred million smokers throghout the world - to plant it with the aid of all the means of modern publicity backed by public money, without knowing for certain that they have anything to be afraid of in the particular habit against which thepropaganda is to be directed. After all, a large n umber of the smokers of the world are not very clever, perhaps not very strong-minded. the habit is an insidious one difficult to break, and consequently in many, many cases there would be implanted what a psychologist might recognizze as a grave conflict.


Sir Ronal Fisher, 1958
http://www.york.ac.uk/depts/maths/histstat/fisher272.pdf


"Love is most nearly itself when here and now cease to matter".
T.S. Eliot

EBHC

Therapies
Dr Bob Phillips
Junior Fellow, Centre for Evidence-based Medicine, Oxford


Therapy
 Ask a question
 Acquire some articles
 Appraise the evidence
 Apply the findings
 Assess your performance
Therapies
 To treat or not to treat?

 Validity
 Importance
 Applicability
Therapies
 Validity
• Was it randomised?
• Was the allocation concealed?
• Were the all the subjects analysed correctly?

• Was it blinded?
• Were the groups similar?
Therapies
 Importance
• What were the results?
• Over what time period?
• With what precision?

Therapies
Number needed to treat
Relative risk reduction
Absolute risk reduction
Event rates
Therapies
Event rates
n with event / total

Control event rate (CER)
Experimental event rate (EER)
Therapies
Absolute risk reduction
difference in two event rates
CER - EER = ARR

Relative risk reduction
proportion of control rate
CER-EER / CER = RRR

Therapies
Number needed to treat
number of extra patients you need to treat to prevent one bad outcome
1 / ARR = NNT
Therapies
95% confidence interval
range within which the true value falls with 95% confidence

use computer (e.g. CATMaker)

Therapies
Application
Can it be applied to my patient?
Can it be done here?
How do patient values affect the decision?
Therapies
Is it valid?
Is it important?
NNT for what
over how long
with what precision
Does it apply?

Therapies
Dr Bob Phillips
Junior Fellow, Centre for Evidence-based Medicine, Oxford

An offset in Response-Variable Type

Response-variable type

The following response (y-variable) types are commonly encountered:

ñ ‘continuous’ (measurements etc.)
ñ counts (of events etc.)
ñ categorical
ñ binary
ñ nominal
ñ ordinal
ñ durations (survival or event-history data)

Mixture of continuous and discrete (e.g., where response is
either zero or a positive amount of something) sometimes occurs, and demands special care.

Response type: continuous

If a model is required for E(y), consider GLM with suitably-chosen link function.
Alternatively, use a linear model, possibly after a non-linear transformation of y.

GLM has advantage of allowing variance to depend on mean in a specified way. For example, with homogeneous multiplicative errors, variance = [E(y)]2.

In a GLM (or GAM) the link function is chosen to achieve linearity (additivity) of the right hand side. Often (but not necessarily) this means linking the mean in
such a way that g[E(y)] can take any real value. For example, if E(y) > 0, g(μ) = log μ will often be a candidate.

Response type: counts

e.g., numbers of arrests made by different police forces in different time periods.
Interest is most often in the rate of occurrence per unit of exposure, where ‘exposure’ might be amount of time, population at risk, person-hours of effort, or a composite.

Most natural starting point is a Poisson model with log link:
yi  Poisson(μi), with, say,
log μi = log ti + 0 + 1xi + 2zi

where ti is the known exposure quantity for the ith count.

The term log ti here, with no unknown coefficient attached to it, is called an offset. It ensures that the other effects are all interpretable as rate-multipliers.

Source: http://springschool.politics.ox.ac.uk/archive/index.asp

ASK Oxford