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PubMed2002

Meta-analysis combining parallel and cross-over clinical trials. I: Continuous outcomes.

Among clinical trials assessing a given treatment, often parallel and cross-over designs are used together. In the first paper of a series of three, we explore two methods to pool continuous outcomes in a meta-analysis combining parallel and cross-over trial designs: the weighted mean difference (WMD) and the standardized weighted mean difference (SWMD). The combined design meta-analytic formulae are based on a weighted average of the two design treatment estimates. A random effects model can be implemented. Both WMD and SWMD can be used, the choice of the method is determined by the type of outcomes obtained in the trials. Compared to the number of included subjects, the relative weight of the cross-over design is large in combined-design meta-analysis. Differences in the weight estimation between WMD and SWMD can also accentuate the relative weight of cross-over trials, which must be considered a case of design-specific bias.

Blood Pressure↗
PubMedDate not supplied

The value of specialized tests in studies where ordered group means are expected.

The performances of three tests for ordered means (Bartholomew's, Williams' and a modified method of least significant differences) are compared with the performances of more general multiple comparison procedures. The tests are assessed using simulated data representing various patterns of results from a toxicological study with one (zero dose) control group and three treatment groups. The specialized tests are considerably more powerful than the general tests and their application is recommended whenever ordered group means are expected.

Analysis of Variance↗
PubMed1989

The use of baselines in clinical trials of bronchodilators.

Two important qualities of controlled clinical trials are that they reduce dependence on historical standards for evaluating therapy and separate the effect of treatment from the confounding influence of time. Whatever the theory of the clinical trial, however, time has not easily been banished from the analysis of medical experiments in practice, and many doctors still prefer to evaluate treatments by comparing now with then rather than treatment with control. This is especially so in trials of bronchodilators in the treatment of asthma where, it is shown, baselines are used in ways which can increase the variability of measurement and even bias the results.

Asthma↗
PubMedDate not supplied

Sickle cell anaemia trial.

The major cause of death in sickle cell anaemia is from infection, especially infection caused by Streptococcus pneumoniae. Meningitis, pneumonia and septicaemia caused by this organism are the primary types of infection leading to death. Children under three years of age are at highest risk. We have known for over twenty years that approximately 30 per cent of the infants born with sickle cell anaemia will become infected in the first three years of life and one-third can be expected to die from the infection. These data were the reason that we conducted the Prophylactic Penicillin Study (PROPS), a trial to investigate the effectiveness of oral prophylactic penicillin in preventing severe infection due to S. pneumoniae. This investigation was a very efficient, cost effective study because of its timeliness and its conduct within the framework of an ongoing study. Moreover, the question being answered was simple and focused with up-to-date data that permitted accurate estimates of sample size and incidence.

Anemia, Sickle Cell↗
PubMed1991

Analysis of the crossover design in the presence of residual effects.

When a residual effect is suspected in a two-period crossover trial, an analysis of the first-period data is often chosen instead of the potentially biased crossover analysis. This paper indicates how the usual crossover test has to be interpreted correctly and that its bias has two different consequences, namely a conservative or a liberal test decision if a positive (carryover) or a negative (withdrawal) residual effect exists. A multiple testing procedure is presented allowing for simultaneous crossover and first-period analysis controlling the experimental error rate. This procedure together with the correct interpretation of the crossover test enables many useful applications of crossover designs.

Bias↗
PubMed2001

Tests for 2 x K contingency tables with clustered ordered categorical data.

Ordered categorical data summarized in a 2 x K table usually consist of two-sample multinomial or K-sample binomial observations. In analysing these data, we usually assign scores to the K columns and perform a testing for the equality of two multinomial distributions in the former case and no trend among K binomial proportions in the latter case. Among the most popular score tests are the Wilcoxon rank sum test and the Armitage's linear trend test. In this paper we extend the score tests to be used for clustered data under diverse study designs. Our methods do not require correct specification of the dependence structure within clusters. The proposed tests are based on the asymptotic normality for large number of clusters and are a generalization of the standard tests used for independent data. Simulation studies are conducted to investigate the finite-sample performance of the new methods. The proposed methods are applied to real-life data.

Amoxicillin↗
PubMed2001

A general family of distributions for longitudinal dependence with special reference to event histories.

Event histories play an increasingly important role in medical studies. Examples include times between recurrences of tumours, as with bladder cancer, and between repeated infections, as with chronic granulotomous disease. A general method for generating new distributions is proposed by introducing an intensity function into a density. This procedure yields, as special cases, several distributions already proposed in the literature. The families of distributions based on the Pareto distribution are of particular interest for event history analysis because of their relationship to the Laplace transform of a gamma distribution. They can yield multivariate distributions, with longitudinal (serial) dependence by a procedure similar to updating in the Kalman filter and with uniform dependence in a similar way to copulas. For longitudinal dependence, several such updating procedures are proposed.

Antineoplastic Agents, Alkylating↗