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Category Archives: Medical Statistics

Assumptions for Common Statistic Procedures


Observational Studies and Designed Experiments Besides classifying statistical studies as either descriptive or inferential, we often need to classify them as either observational studies or designed experiments. In an observational study, researchers simply observe characteristics and take measurements, as in a sample survey. In a designed experiment, researchers impose treatments and controls and then observe […]

Chi-Square Goodness-of-Fit Test


The statistical-inference procedures discussed in this thread rely on a distribution called the chi-square distribution. A variable has a chi-square distribution if its distribution has the shape of a special type of right-skewed curve, called a chi-square curve. Actually, there are infinitely many chi-square distributions, and we identify the chi-square distribution in question by its […]

Factorial Designs


In this section we will describe the completely randomized factorial design. This design is commonly used when there are two or more factors of interest. Recall, in particular, the difference between an observational study and a designed experiment. Observational studies involve simply observing characteristics and taking measurements, as in a sample survey. A designed experiment […]

Analysis of Variance


Analysis-of-variance procedures rely on a distribution called the F-distribution, named in honor of Sir Ronald Fisher. A variable is said to have an F-distribution if its distribution has the shape of a special type of right-skewed curve, called an F-curve. There are infinitely many F-distribution (and F-curve) by its number of degrees of freedom, just as we […]

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, […]