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Biomedical subjects

D J Hand

Publications and source records attributed to D J Hand.

17 recordsLinked to original sources
PubMed1992

Statistical methods in diagnosis.

Motivations are presented for exploring formal statistical methods for use in medical diagnosis and the advantages and disadvantages are discussed. A brief review is presented of classical linear discriminant analysis, quadratic discriminant analysis, logistic regression, nearest neighbour and kernel methods, recursive partitioning methods, the independence model, regularized discriminant analysis, structured conditional probability distributions, methods for categorical data, and other methods. Criteria on which a choice might be made are presented and methods for assessing diagnostic performance are outlined. Particular applications of screening and chromosome analysis are used as illustrations and available software is described.

Bayes Theorem↗
PubMed1992

Effects of treatments by calcium and sex hormones on vertebral fracturing in osteoporosis.

Lateral radiographs of the thoracic and lumbar spine were taken periodically in 49 patients with osteoporosis. Thirty patients were postmenopausal, and 19 nonmenopausal with osteoporosis due to steroids, male hypogonadism, alcoholism, thyrotoxicosis or unknown cause. Patients were studied before, during and after treatment with high calcium alone, or with combined calcium and sex steroids. Calcium was given as effervescent calcium lactate gluconate, and sex hormones as oestradiol valerate, testosterone oenanthate, or methenolone oenanthate. A total of 964 films covering 409 patient-years were available for measurement. On each vertebra, deformity due to loss of anterior height was measured and assigned to one of four grades. For the time interval between each consecutive pair of films, a patient's vertebral fracture rate score was calculated and expressed per thousand patient-years. In comparison with the corresponding pretreatment fracture rate score, both the postmenopausal and the nonmenopausal groups who had not received sex hormones previously, failed to show significant changes (p = 0.144; p = 0.017) on high calcium alone during mean periods of 4.3 and 2.8 years respectively. If the first 2 years on high calcium were excluded for the postmenopausal group, they still failed to show a reduction in fracture rate score (observed for a mean period of 5.0 years; p = 0.04). When treated with combined calcium and sex hormones, both postmenopausal and nonmenopausal groups showed a lower fracture rate score of 20 and 207 respectively when compared with the pretreatment levels of 1500 and 1697 (in mean treatment periods of 3.2 and 4.4 years; p less than 0.001 in each case). When given high-dose calcium alone, but after treatment with sex hormones as well, the postmenopausal group showed no change in fracture rate score from pretreatment (in a mean of 3.1 years; p = 0.069); however the nonmenopausal group still showed a significant reduction in fracture rate score from 1697 to 42 over a mean period of 2.3 years (p = 0.001). The postmenopausal group, after stopping all treatment, showed a higher fracture rate score of 1286 (in a mean of 2.6 years) than did those on combined calcium and sex hormones, in whom the fracture rate score was 20 (in a mean of 3.2 years; p = 0.008). A subgroup of 11 patients with osteoporosis of both the menopausal and nonmenopausal types, had data both before (in a mean of 5.5 years) and during (for a mean of 2.5 years) treatment with calcium alone; the fracture rate scores were 1473 and 918 (p = 0.247).(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1991

Contradictory correlations between derived scales.

In a clinical trial one scale of pain relief is scored backwards relative to another (high on one corresponding to low on the other), with a consequent large negative correlation. But two derived scales of total pain, obtained by multiplying average pain relief on each scale by duration of pain (common to both pain relief measurements) gave an almost zero correlation. This apparent contradiction is explained by the inverse relationship between the pain relief scales and the large differences in duration of pain experienced by the patients.

Clinical Trials as Topic↗
PubMed1991

Screening for vertebral osteoporosis using individual risk factors. The Multicentre Vertebral Fracture Study Group.

Osteoporosis is a major cause of ill health in postmenopausal women. Several risk factors for osteoporosis have been identified, and they have been widely recommended as a means of identifying subgroups of postmenopausal women who might benefit from prophylaxis and therapy. Evidence to support this use of risk factors is currently lacking, however. We have constructed and evaluated a profile of putative risk factors as a means of identifying women attending general practitioners who have sustained vertebral fractures. The overall prevalence of vertebral fractures in the 1012 women (mean age 64.4 years) studied was 7.8%. Women who had sustained vertebral fractures in this population were significantly (p less than 0.05) older and shorter than those without fractures. They reported a significantly (p less than 0.05) earlier menopause, lower parity and a greater prevalence of hyperthyroidism. However, the best screening instrument devised was not sufficiently predictive to warrant widespread use.

Aged↗
PubMed1985

Who gets renal bone disease before beginning dialysis?

To identify patients at risk from renal bone disease we compared the demographic characteristics of 243 patients with end stage renal failure grouped according to the presence (97 (40%] or absence of severe renal bone disease as judged by histological criteria. Youth, female sex, tubulointerstitial types of nephropathy, and a long duration of uraemia were all identified as significant independent risk factors for the development of bone disease. The relative risks from being female and having tubulointerstitial renal disease were separately identifiable when the estimated observation of renal failure was short (less than four years). The identification of patients at high risk from bone disease may clarify the pathogenesis and treatment strategies of renal osteodystrophy.

Adolescent↗
PubMed1983

A comparison of two methods of discriminant analysis applied to binary data.

The results of applying classical linear discriminant analysis and kernel discriminant analysis to several real sets of multivariate binary data are presented. Classical discriminant analysis is intrinsically parametric and is usually presented as being well-suited to continuous variables; it is also well-known to be optimal when the (two) classes have normal distributions with identical covariance matrices. The kernel method, on the other hand, is nonparametric and, in the form used here, is ideally suited to binary data. The apparent error rates of the kernel method are found to be consistently less than those of the classical method. However, when the true error rates are estimated either by applying the classifiers to independent test sets, or by the leaving-one-out method from the design sets, no significant difference is discernible between the two types of classifier.

Enuresis↗
PubMed1982

Statistical tests in experimental psychiatric research.

It is pointed out that the subjects used in psychiatric research experiments are usually drawn in such a way as to invalidate many of the commonly applied statistical tests. The necessarily non-statistical component of any inference is noted, and the area where one might hope for an exact statistical inference is identified. A class of tests permitting such inferences is described. Their theoretical and practical advantages are outlined.

Humans↗
PubMed1980

Aircraft noise and mental health: I. Prevalence of individual symptoms.

A domiciliary survey (sample size circa 6000) was conducted in areas of different aircraft noise exposure affected by London (Heathrow) Airport. Respondents were urban dwellers age 16+. Since no differences were found in the prevalence of manifest psychiatric disorders, the frequency of 27 individual acute and chronic symptoms was investigated. Many acute symptoms showed an increase with noise, and this was particularly evident for waking at night, irritability, depression, difficulty in getting to sleep, swollen ankles, burns/cuts/minor accidents, and skin troubles. Two chronic symptoms, tinnitus and ear problems, showed evidence of an increase with noise, while most other chronic symptoms were more common in low noise conditions. Results are controlled for the effects of age, sex and other standard epidemiological variables. Irrespective of their association with noise, most symptoms, chronic and acute, were more frequent among those respondents who also reported high annoyance. Suggestions for the analysis of surveys of health effects by noise are put forward.

Accidents↗
PubMed1979

Comparison of three studies of aircraft noise and psychiatric hospital admissions conducted in the same area.

Two earlier studies conducted in the vicinity of London (Heathrow) Airport compared the rate of admissions to a psychiatric hospital from areas exposed to different levels of aircraft noise. Their methods and results were not identical. A third study, reported here, examined standardized rates of admission to the same hospital for a longer period and for a larger area divided into 4 bands of aircraft noise. Statistically significant trends of decreasing admission with increasing noise levels were found. Comparisons between the investigations show how the contradictory results are related to the methods used and the accuracy of the data, and that caution should be exercised in formulating conclusions from exploratory research.

Aircraft↗
PubMed1979

Validity and uses of a screening questionnaire (GHQ) in the community.

The 30-item General Health Questionnaire (GHQ) has been validated against the criterion of a standardized psychiatric interview in the community. Used for screening, the GHQ misclassified 25 per cent of 105 respondents, being worse for men. Specificity and sensitivity were above .70. The alternative use of the GHQ as an estimator and as an indicator of morbidity in epidemiological surveys is described and discussed.

Epidemiologic Methods↗