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Category Archives: Clinical Research

The Logic Behind Meta-analysis – Random-effects Model


The fixed model starts with the assumption that true effect size is the same in all studies. However, in many systematic reviews this assumption is implausible. When we decide to incorporate a group of studies in a meta-analysis, we assume that the studies have enough in common that it makes sense to synthesize the information, […]

The Logic Behind Meta-analysis – Fixed-ffect Model


Overview Most meta-analyses are based on one of two statistical models, the fixed-effect model or the random-effects model. Under the fixed-effect model we assume that there is one true effect size (hence the term fixed effect) which underlies all the studies in the analysis, and that all differences in observed effects are due to sampling […]

Conceiving the Research Question and Developing the Study Plan


The research question is the uncertainty that the investigator wants to resolve by performing his/her study. There is no shortage of good research questions, and even as we succeed in answering some questions, we remain surrounded by others. Clinical trials, for example, established that treatments that block the synthesis of estradiol (aromatase inhibitors) reduce the […]

Outline of A Study


This is the one-page study plan of a project carried out by Valerie Flaherman, MD, MPH, begun while she was a general pediatrics fellow at UCSF. Most beginning investigators find observational studies easier to pull off, but in this case a randomized clinical trial of modest size and scope was feasible, the only design that […]

Basic Concepts in Statistics


Three Kinds of Data There are three types of data, including interval data where some variables are measured on a scale with constant intervals, nominal/categorical data, and ordinal data. For interval data, the absolute difference between two values can always be determined by subtraction. Interval variables include some such as tempterature, blood pressure, height, weight, […]