Biomedical subjects

D A Grayson

Publications and source records attributed to D A Grayson.

12 recordsLinked to original sources

PubMed1990

The matter of scale.

The genetic (and environmental) picture that emerges from a behavior genetic analysis is acknowledged to be a function of the scale upon which the particular trait being analyzed is measured. Differing views exist about how such data should be interpreted. The aim of the present paper is to air such issues and to emphasize that the reporting of substantive results, e.g. in psychiatric studies, should make clear that results are scale dependent, as this qualification may not be apparent to a psychiatric readership.

Animals↗

PubMed1989

Twins reared together: minimizing shared environmental effects.

The assumption that genetic variance is primarily (if not all) additive is usually made in biometric-genetic analyses of data collected on twins raised together. It is known amongst those familiar with twin methods that this assumption may lead to overestimates of heritability and under-estimates of shared environmental variance (E2), although this limitation is not always made clear to genetically native readers of such applications. The concept of "emergenic" genetic mechanisms (a potentially extreme epistatic or nonadditive mechanism) discussed by Lykken (1982) raises the possibility that genetic variance may be substantially nonadditive in some applications. The aims of the present paper are to investigate the potential size of such nonadditivity and such misestimations and to provoke discussion on the empirical plausibility (or otherwise) of epistatic effects. For if substantially present, the results of conventional twin analyses are substantially biased.

Genetic Variation↗

PubMed1988

Limitations on the use of scales in psychiatric research.

This paper discusses some issues involved in the construction and interpretation of scales in psychiatric research. The issues covered include scale construction, measures of scale homogeneity, the logic of factor analysis and the interpretation of effects manifesting in scale-data, especially interaction effects. The aim of the paper is to "de-mystify" some of the psychometric techniques commonly available, and to emphasize that their appropriate use depends on both a firm understanding of the content area to which they are applied and a rudimentary knowledge of what the methods purport to do.

Depressive Disorder↗

PubMed1987

The relationship between symptoms and diagnoses of minor psychiatric disorder in general practice.

In an earlier paper (Goldberg et al. 1987) 36 common symptoms of minor psychiatric disorder in general practice were analysed using the technique of latent trait analysis. From this analysis two dimensions of illness emerged, corresponding to anxiety and depression. In the present paper, this symptom-based representation of minor psychiatric illness is used as a framework for comparing four diagnostic systems: General Practitioner (GP) diagnoses, the ID-CATEGO diagnostic system, the DSM-III system and the Bedford College diagnostic system. This analysis clarifies the reasons for disagreement among systems of diagnostic criteria and examines the practical effects of alternative diagnostic algorithms.

Anxiety Disorders↗

PubMed1987

Diagnoses of dementia and depression: a latent trait analysis of their performance.

Four diagnostic systems for dementia and depression are compared on a community sample of 274 subjects. They are: DSM-III, Gurland's system, AGECAT and a clinician's ratings. These are compared, not in the usual terms of prevalence rates and cross-tabulations of diagnostic categories, but by examining the performance of each system in terms of hypothetical, continuously distributed traits underlying the symptoms of dementia and depression, as in the latent trait model described by Duncan-Jones et al. (1986). Each diagnosis is characterized by the level of severity (threshold) at which it operates, and its accuracy. Evidence is given to support a dimensional view of dementia.

Aged↗

PubMed1987

Confounding confounding.

Miettinen and Cook (Am J Epidemiol 1981;114:593-603) postulate that confounding is a result of exposure-strata dependence in the joint source population, irrespective of the effective parameter used. Boivin and Wacholder (Am J Epidemiol 1985;121:152-8) postulate that confounding is dependent on the additive structure of the crude effect parameter. Both of these conflicting principles are at variance with the familiar definition in terms of parameter bias. It is argued that the change-in-parameter definition is the only fundamental definition.

Epidemiologic Methods↗

PubMed1987

Can categorical and dimensional views of psychiatric illness be distinguished?

Bimodality in a distribution of symptoms is often claimed to be convincing evidence that a disorder is categorical, a discrete disease entity, rather than the extreme on a continuous dimension. However, using concepts from contemporary psychometric theory it is shown that bimodality can arise from the dimensional viewpoint. In fact, contrary to the usual belief, bimodality would be expected to occur in many research contexts if the dimensional alternative were correct.

Humans↗

PubMed1987

Statistical diagnosis and the influence of diagnostic error.

The optimal class of rules for allocating subjects, on the basis of an observable symptom profile, to sick or well states is based on the likelihood-ratio scale. This scale is estimated from a training set where the symptoms and true disease status are simultaneously measured. In the important case where true disease status is unavailable and only a "noisy" diagnosis can be performed, it is shown that exactly the same optimal class of allocation rules is obtained. This is true under very general assumptions of diagnostic error. Special cases are examined, providing insight into the dynamics of such diagnostic error. In particular, the conditions under which sensitivity, specificity, and the overall correct classification rate are underestimates of the true quantities are investigated.

Biometry↗

PubMed1986

Latent trait analysis of the Eysenck Personality Questionnaire.

This paper exhibits contemporary psychometric models of questionnaires with dichotomous items. Such as approach allows assessment of individual items in terms of precision of measurement in ways not previously available. This Latent Trait Model approach is used to analyse the responses of 3806 subjects to the Eysenck Personality Questionnaire (EPQ). Short forms, of 10 items length, are recommended; they are the best possible such short forms, in that they provide the most accurate possible measurement overall.

Humans↗

PubMed1986

Social support, dementia and depression among the elderly living in the Hobart community.

In a community sample of the elderly (N = 274) in Hobart, Tasmania, cases of dementia and depression were ascertained by the Canberra Geriatric Mental State and the Mini Mental State Examination. Social relationships and support were examined by means of the Interview Schedule for Social Interaction. The elderly had fewer social relationships than younger adults, but were more content with what they did have. Elderly women had more affectional ties than elderly men. The presence of offspring in the same town increased the number of close ties and of social relationships, but was more important for men than for women. Persons with cognitive impairment or an established dementia reported that they had less social interaction than they would like. Depressed subjects reported having markedly less social interaction than the mentally healthy elderly, but did not complain that it was too little. This study provides a systematic description of the social environment of the elderly, both in mental health and in states of depression or impaired cognition.

Aged↗

PubMed1986

The utility of latent trait models in psychiatric epidemiology.

Latent trait modelling is a recent psychometric technique with great potential for the construction and refinement of psychiatric instruments. It provides a greater insight into the nature of measurement in psychiatry and the statistical machinery for improving it. This expository paper starts with a non-technical outline of the latent trait model, gives a detailed analysis of the 12-item General Health Questionnaire (GHQ) and examines points raised by the empirical analysis through computer stimulation. It is shown that the latent trait model can give a good representation of empirical data and uncover new aspects of a familiar instrument. It provides a precise methodology for evaluating the functioning of a questionnaire and for developing better short instruments. It highlights the need, and provides the means, to tailor instruments for different tasks, such as (a) screening, and (b) measuring over the whole range of the population. We examine scoring in the light of the model, and show that simple scoring is often adequate. While points for further methodological development are noted, it is argued that the method is already sufficiently developed for general application.

Adaptation, Psychological↗

PubMed1985

Dementia and depression among the elderly living in the Hobart community: the effect of the diagnostic criteria on the prevalence rates.

A survey was made of 274 non-institutionalized persons aged 70 and over living in Hobart. The prevalence of dementia and of depression was measured by interviewing subjects using a modified version of the Geriatric Mental State Schedule (GMS) (Copeland et al. 1976) and the Mini Mental State Examination (MMSE) (Folstein et al. 1975). Rates of morbidity were derived from different diagnostic procedures. These were: diagnoses made by a psychiatrist (A.S.H.) directly from the interview schedules and audiotapes, and rated as mild, moderate or severe; the criteria laid down in DSM-III, converted into algorithms describing 3 degrees of severity; and the algorithms for pervasive dementia and depression proposed by Gurland et al. (1983), and from these authors' rational scales. In addition, the relation between scales for dementia and for depression and the diagnosed categories was examined. Some problems in applying these methods to aged persons in the community are discussed. It is concluded that more detailed specification of criteria is desirable if the comparative epidemiology of dementia and depression in old age is to advance.

Aged↗