Logistic regression in case-control studies: The effect of using independent as dependent variables

In case-control studies, cases are sampled separately from controls. In such studies the primary analysis concerns the estimation of the effect of covariables on being a case or a control. To explore causal pathways, further secondary analysis could concern the relationships among the covariables. In this paper the validity of such secondary analysis is addressed. In particular, the use of multiple logistic regression in case-control studies where the dependent variable is not the case/control indicator is explored. It is shown that only under very restrictive conditions will sample regression coefficients correctly estimate their true value. In many situations, it may be valid to regress one covariable on others in the control group, but not in the case group or the combined sample. This principle is illustrated by a study of sexually transmitted disease in Kenya.     

Stable Anticonvulsant Action of Benzodiazepines During Development in Rats

Abstract— The anticonvulsant action of midazolam and clonazepam was studied in 168 immature rats in three age groups (12, 18 and 25 days old). Epileptic after-discharges of the spike-and-wave type accompanied by clonic seizures of facial and forelimb muscles induced by stimulation of sensorimotor cortex were used as a model. The solvent used for clonazepam exhibited a tendency to anticonvulsant action in 12-day-old rats. On the contrary, a proconvulsant action was seen in 25-day-old animals. The action of both benzodiazepines was identical and did not change substantially during development. The highest dose used (1 mg kg^?1, i.p.) shortened the duration of epileptic after-discharges, the two lower doses (0·1 and 0·02 mg kg^?1, i.p.) suppressed the progressive prolongation with repeated stimulations seen under control conditions. Motor correlates of stimulation remained practically uninfluenced by the two benzodiazepines, myoclonic seizures accompanying epileptic after-discharges were attenuated by the highest dose of both drugs.     

Septo-optic dysplasia: MR imaging

Septo-optic dysplasia is the diagnosis when optic nerve hypoplasia is seen in conjunction with dysgenesis of the septum pellucidum. Nearly two-thirds of these patients have hypothalamic-pituitary dysfunction, and half have schizencephaly. The disorder is difficult to classify because of the diversity of clinical and pathologic manifestations. Magnetic resonance images of 11 patients with clinical and radiographic evidence of septo-optic dysplasia were reviewed retrospectively. The "syndrome" appears to include two subsets of patients whose abnormalities have different embryogenesis and neuropathologic findings. The existence of these two subsets helps to explain the diversity of the clinical and radiologic findings.     

Epitope-specific humoral immunity to Plasmodium vivax Duffy binding protein

Erythrocyte invasion by Plasmodium vivax is completely dependent on binding to the Duffy blood group antigen by the parasite Duffy binding protein (DBP). The receptor-binding domain of this protein lies within a cysteine-rich region referred to as region II (DBPII). To examine whether antibody responses to DBP correlate with age-acquired immunity to P. vivax, antibodies to recombinant DBP (rDBP) were measured in 551 individuals residing in a village endemic for P. vivax in Papua New Guinea, and linear epitopes mapped in the critical binding region of DBPII. Antibody levels to rDBP(II) increased with age. Four dominant linear epitopes were identified, and the number of linear epitopes recognized by semi-immune individuals increased with age, suggesting greater recognition with repeated infection. Some individuals had antibodies to rDBP(II) but not to the linear epitopes, indicating the presence of conformational epitopes. This occurred in younger individuals or subjects acutely infected for the first time with P. vivax, indicating that repeated infection is required for recognition of linear epitopes. All four dominant B-cell epitopes contained polymorphic residues, three of which showed variant-specific serologic responses in over 10% of subjects examined. In conclusion, these results demonstrate age-dependent and variant-specific antibody responses to DBPII and implicate this molecule in partial acquired immunity to P. vivax in populations in endemic areas.     

The effect on grades of the timing and site of third-year internal medicine clerkships

Two important factors affecting the performances of third-year medical students on their basic internal medicine clerkships were investigated: (1) the effect on their grades of when in the academic year they took the internal medicine clerkship, and (2) the effect on their grades of the site of the clerkship. During the academic years 1983-84, 1984-85, and 1985-86, the Department of Internal Medicine of the University of Illinois College of Medicine at Chicago conducted 12-week junior clerkships at six hospital sites. The study analyzed the 535 students' subjective grades, clerkship examination scores, final grades, and National Board of Medical Examiners Part I (NBME-I) scores. Although students' performances as characterized by subjective evaluations did not improve as the academic year progressed, mean scores on clerkship examinations improved steadily during the same period. The site of the clerkship, whether a community-affiliated hospital or a medical center hospital, affected neither subjective nor objective grades.     

Relative Immunogenicity and Tolerogenicity of Individual Regions or Segments of the MHC

Mixed lymphocyte culture (MIX) reactivity, induction of cytotoxicity in vitro, survival of skin allografts, and induction of neonatal transplantation tolerance were compared in mice of the strain combinations differing in the entire H-2 complex or in individual segments of it. The results showed that antigenic products of the K end of the H-2 complex were more immunogenic and also more resistant to tolerance induction than the products of the D end of H-2. I-region products that elicited transplantation reactions of variable strength, depending on the detection system, were relatively easier to overcome in tolerance induction and could, at least in some combinations, contribute to tolerance induction across the barrier represented by the products of the K region of the H-2 complex.