Re: Ecologic studies--biases, misconceptions, and counterexamples.
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Bias↗
Biomedical subjects
V Lasserre
Publications and source records attributed to V Lasserre.
Double-blind comparison of an acetaminophen 400 mg-codeine 25 mg combination versus aspirin 1000 mg and placebo in acute migraine attack.
The purpose of this study was to compare the efficacy and tolerance of a single dose of the acetaminophen 400 mg-codeine 25 mg combination (ACC) aspirin 1000 mg (A) and a placebo (P) for the treatment of acute migraine attack. The study design was randomized, multicentre, double-blind and double dummy with cross-over on three periods. Of the 198 patients who had three attacks 29.8%, 52.3% and 49.7% had recorded the complete or almost complete disappearance of the pain at 2 h after P, A and ACC respectively. When compared with the placebo, the difference was significant for the A and ACC. When complete disappearance of pain at 2 h was used as a criterion, no significant difference was observed. These results enabled the sensitivity of the evaluation criteria suggested for clinical trials of migraine attack to be discussed.
Acetaminophen↗
Occupational risk factors for acute leukaemia: a case-control study.
A case-control study has been performed for occupational risk factors of acute leukaemia, based on 185 cases more than 30 years old and 513 matched controls. There was a significant excess of polyvalent farming and electronic engineers among professions of cases, and, in addition of metal workers when considering the professions pursued for more than 5 years. The corresponding exposures were analysed through a detailed questionnaire, and assessed by an industrial hygienist after blinding the case-control status. The odds ratios (OR) were computed after adjustment on matching variables and prior chemo- or radiotherapy treatment, and after stratification for the level and total duration of exposure. There was no excess of professional exposure to ionizing radiation among cases. A significant relationship was observed between acute leukaemia and high or medium exposure to benzene, as well as over 10 years high or medium exposure to exhaust gas. In addition a significant relationship was observed with exposure to pesticides--insecticides and/or weed killers--and to electric and magnetic fields (EMF). The relationship with pesticides was significant when considering high or medium exposure to weed killers and more than 10 years exposure to both subtypes of pesticides. The relationship with pesticides and EMF remained significant when confounding factors were taken into consideration and after adjustment on co-exposure to benzene. The cytological studies showed that acute leukaemias following exposure to benzene (high or medium) and to EMF were only of myelogenous subtypes, whereas those following exposure to pesticides were divided between lymphoblastic and myeloblastic subtypes. Cytogenetic studies failed to show increased frequency of chromosomal abnormalities, as described in acute leukaemias secondary to anti-cancer treatments. Our study adds credence to the hypothesis that pesticides and EMF are leukaemogenic agents, together with benzene.
Acute Disease↗
Determination of optimal designs using linear models in crossover trials.
This study determines the optimal designs for crossover trials with fixed size of population, in order to estimate contrasts between two treatment effects, for various numbers of periods. The problem is approached in the framework of a linear model, taking into consideration the structure of a variance matrix constructed from two random sources: linked-to-subject random effect and linked-to-measurement random error. Different models, as well as different optimality criteria, are considered. For example, when two periods are planned, for the criterion of the minimization of the variance of the treatment-effect estimator, in the presence of residual effect, the optimal design corresponds to four groups of sequences, (T1, T2), (T2, T1), (T1, T1), (T2, T2); without residual effect it corresponds to two groups, (T1, T2), (T2, T1). Optimal designs are given for the comparison of two treatments when using three or four periods.
Clinical Trials as Topic↗