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Category Archives: Evidence-Based Medicine

The Logic Behind Meta-analysis – Random-effects Model

25-Dec-17

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

19-Dec-17

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 […]

Linear Regression

16-Oct-17

The Regression Equation When analyzing data, it is essential to first construct a graph of the data. A scatterplot is a graph of data from two quantitative variables of a population. In a scatterplot, we use horizontal axis for the observations of one variable and a vertical axis for the observations of the other variable. […]

Inferences for Population Standard Deviations

05-Oct-17

Inferences for One Population Standard Deviation Suppose that we want to obtain information about a population standard deviation. If the population is small, we can often determine 𝜎 exactly by first taking a census and then computing 𝜎 from the population data. However, if the population is large, which is usually the case, a census is […]

Inferences for Population Proportions

24-Sep-17

Confidence Intervals for One Population Proportion Statisticicans often need to determine the proportion (percentage) of a population that has a specific attribute. Some examples are: the percentage of U.S. adults who have health insurance the percentage of cars in the United States that are imports the percentage of U.S. adults who favor stricter clean air […]