Baseline The baseline mean (mean under H 0) is the number one would expect to see if all experiment participants were assigned to the control group. The sample size and power calculator uses the Z-distribution (normal distribution).ģ. One can also calculate power and sample size for the mean of just a single group. See Absolute versus relative difference for additional information. height, weight, speed, time, revenue, etc.), or the relative difference between two proportions or two means (percent difference, percent change, etc.).
conversion rate or event rate), the absolute difference of two means (continuous data, e.g. The outcome of interest can be the absolute difference of two proportions (binomial data, e.g. Power calculations are not currently supported for more than one treatment group due to their complexity.Ģ. These are only approximately accurate and subject to the assumption of about equal effect size in all k groups, and can only support equal sample sizes in all groups and the control. For comparing more than one treatment group to a control group the sample size adjustments based on the Dunnett's correction are applied. The sample size calculator supports experiments in which one is gathering data on a single sample in order to compare it to a general population or known reference value (one-sample), as well as ones where a control group is compared to one or more treatment groups ( two-sample, k-sample) in order to detect differences between them. Parameters for sample size and power calculationsġ. Usually one would determine the sample size required given a particular power requirement, but in cases where there is a predetermined sample size one can instead calculate the power for a given effect size of interest. It can be used both as a sample size calculator and as a statistical power calculator. This calculator allows the evaluation of different statistical designs when planning an experiment (trial, test) which utilizes a Null-Hypothesis Statistical Test to make inferences. Absolute versus relative difference and why it matters for sample size determination.Types of null and alternative hypotheses in significance tests.Why is sample size determination important?.
Parameters for sample size and power calculations.Using the power & sample size calculator.The graphing of epidemic curves was a popular feature (despite an optical illusion caused by the diagonal line pattern). This provided a means of distribution that did not require copying by CDC office staff or permission to distribute through government channels.
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The programs and manual remained in the public domain, but copies were also marketed by a commercial firm in Atlanta -USD, Inc.- without any special arrangement with CDC. Suggestions came from users in the field and were rapidly incorporated into new versions of the software.ġ988 Epi Info™, Version 3, came with a 150-page manual, enhanced statistics, and sample programs, including two outbreaks and a surveillance system. The first versions of Epi Info™ were distributed by Andy, Jeff, and Tony from their office. Note the negative chi square, probably a result of limitations in integer values in an early version of Turbo Pascal. The TABLES command began to offer statistical output. 1987 Epi Info™, Version 2, had a bound manual of 112 pages, a pulldown menu, the EPED word processor for creating questionnaires, ENTER, ANALYSIS, an epidemiologic calculator called STATCALC, EPICURVE for plotting histograms, a MERGE program, and IMPORT and CONVERT programs for file conversions.
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