Antibodies to a variety of foods, and in particular cereals, were measured in serum from 100 patients with acute psychoses and 100 elective surgical patients. For 13 out of 14 foods to which non-IgE antibodies were detected the schizophrenics had slightly more antibodies than the controls. There was an association between a possible secondary mania and the presence of IgE antibodies to wheat or rye. However, neither the schizophrenia nor the mania findings can be regarded as evidence for food allergy causing psychiatric disorder, since the immunological findings in both cases may represent consequences of the illnesses or their treatment, rather than causes of the illness.

It is argued that a general practitioner's ability to make accurate ratings of psychological distress is partly determined by the rate at which patients emit cues that are indicative of such distress. This study addresses the behaviours of doctors which influence the rates at which patients emit such cues. Consultations were videotaped involving six General Practice Vocational Trainees, three of them poor, and three of them able identifiers of emotional illness. Consultations were selected so that each trainee was rated interviewing 4 patients with low GHQ scores, and 4 patients with high scores. Behaviours are described which lead to increased cue emission and which are also practised more frequently by able identifiers, while other behaviours reduce cue emission and are practised less frequently by them. Another set of behaviours is no more frequent among the able identifiers, but when practised by able identifiers is associated with increased cue emission by the patients, and when practised by poor identifiers with unaltered or decreased cue emission. Interviews that are ‘patient-led’ are associated with increased rates of cue emission, while those that are ‘doctor-led’ are associated with lower rates. The implications of these findings for training doctors working in general medical settings are discussed.

Background. Previous epidemiological studies indicate large cross-national differences in prevalence of depression.

Methods. At 15 centres in 14 countries, 25916 primary care patients were screened for common mental disorders. A stratified random sample of 5447 primary care patients completed a baseline diagnostic assessment and 3197 completed a 12-month follow-up assessment. Psychiatric symptoms and diagnoses were assessed using the Composite International Diagnostic Interview (CIDI). Interviewer-rated disability was assessed using the Social Disability Schedule (SDS).

Results. Prevalence of current major depression varied 15-fold across centres. When centres were divided into three groups according to prevalence rates, the symptom pattern or latent structure of depressive illness was generally similar at low-, medium-, and high-prevalence centres. Depression was universally associated with disability, but this association varied significantly (t = 3·51, P = 0·0005) across centres. At higher-prevalence centres, depression was associated with lower levels of impairment. At 1 year follow-up, higher prevalence centres had both significantly higher rates of depression onset (t = 3·11, P = 0·002) and higher rates of persistence among those depressed at baseline (t = 2·49, P = 0·013).

Conclusions. Large cross-national variations in depression prevalence cannot be attributed to ‘category fallacy’ (cross-national differences in the nature or validity of depressive disorder). Use of identical measures and diagnostic criteria may actually identify different levels of depression severity in different countries or cultures. Cross-national differences in the onset and outcome of depression may reflect either true prevalence differences or differences in diagnostic threshold.

Background. In other branches of epidemiology, stratum specific likelihood ratios (SSLRs) have been found to be preferable to fixed best threshold approaches to screening instruments. This paper presents SSLRs of GHQ-12 and GHQ-28 and compares the SSLR method with the traditional optimal threshold approach.

Methods. Random effects meta-analysis and meta-regression were used to obtain pooled estimates of SSLRs of the two questionnaires for the 15 centres participating in the WHO study of Psychological Problems in General Health Care. We illustrated the use of SSLRs by applying them to random samples of patients from centres with different backgrounds.

Results. For developed and urban centres, the estimates of SSLRs were homogeneous for 10 out of 12 strata of the GHQ-12 and GHQ-28. For other centres, the overall results, which were heterogeneous for six out of 12 strata, were deemed the currently available best estimates. When we applied these results to centres with different prevalences of mental disorders and backgrounds, the estimates matched the actually observed closely. These examples showed how the SSLR approach is more informative than the traditional threshold approach.

Conclusions. Those working in developed urban settings can use the corresponding SSLRs with reasonable confidence. Those working in non-urban or developing areas may wish to use the overall results, while acknowledging that they must remain less certain until further research can explicate heterogeneity. These SSLRs have been incorporated into nomograms and spreadsheet programmes so that future researchers can swiftly derive the post-test probability for a patient or a group of patients from a pre-test probability and GHQ score.

Background. Different versions of the General Health Questionnaire (GHQ), including the GHQ-12 and GHQ-28 have been subjected to factor analysis in a variety of countries. The World Health Organization study of psychological disorders in general health care offered the opportunity to investigate the factor structure of both GHQ versions in 15 different centres.

Methods. The factor structures of the GHQ-12 and GHQ-28 extracted by principal component analysis were compared in participating centres. The GHQ-12 was completed by 26120 patients and 5273 patients completed the GHQ-28. The factor structure of the GHQ-28 found in Manchester in this study was compared with that found in the earlier study in 1979.

Results. For the GHQ-12, substantial factor variation between centres was found. After rotation, two factors expressing depression and social dysfunction could be identified. For the GHQ-28, factor variance was less. In general, the original C (social dysfunction) and D (depression) scales of the GHQ-28 were more stable than the A (somatic symptoms) and B (anxiety) scales. Multiple cross-loadings occurred in both versions of the GHQ suggesting correlation of the extracted factors. In Manchester, the factor structure of the GHQ had changed since its development. Validity as a case detector was not affected by factor variance.

Conclusions. These findings confirm that despite factor variation for the GHQ-12, two domains, depression and social dysfunction, appear across the 15 centres. In the scaled GHQ-28, two of the scales were remarkably robust between the centres. The cross-correlation between the other two subscales, probably reflects the strength of the relationship between anxiety and somatic symptoms existing in different locations.

Significant progress has been realized in the use of quantum well intermixing (QWI) as a method for tailoring the bandgap energies of optoelectronic devices. Intermixing can be driven by an ion implantation process, an approach that appeals because of its simplicity, its planarity and its adaptability to selective area processing. Despite its success, the advantages of irradiation induced QWI need to be tested further and we report here current results of three research activities which address a) the existence or not of a simple scaling relationship which connects intermixing in a given QW structure for any ion species; b) reproducibility of intermixing in identical QW structures which have been obtained from different growth systems; and c) intermixing for above the well versus through the well implantation.

Background. In recent years the 12-item General Health Questionnaire (GHQ-12) has been extensively used as a short screening instrument, producing results that are comparable to longer versions of the GHQ.

Methods. The validity of the GHQ-12 was compared with the GHQ-28 in a World Health Organization study of psychological disorders in general health care. Results are presented for 5438 patients interviewed in 15 centres using the primary care version of the Composite International Diagnostic Instrument, or CIDI-PC.

Results. Results were uniformly good, with the average area under the ROC curve 88, range from 83 to 95. Minor variations in the criteria used for defining a case made little difference to the validity of the GHQ, and complex scoring methods offered no advantages over simpler ones. The GHQ was translated into 10 other languages for the purposes of this study, and validity coefficients were almost as high as in the original language. There was no tendency for the GHQ to work less efficiently in developing countries. Finally gender, age and educational level are shown to have no significant effect on the validity of the GHQ.

Conclusions. If investigators wish to use a screening instrument as a case detector, the shorter GHQ is remarkably robust and works as well as the longer instrument. The latter should only be preferred if there is an interest in the scaled scores provided in addition to the total score.