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. Power calculations are not currently supported for more than one treatment group due to their complexity.
Type of outcome. The outcome of interest can be the absolute difference of two proportions binomial data, e. See Absolute versus relative difference for additional information. One can also calculate power and sample size for the mean of just a single group.
The calculator uses the Z-distribution normal distribution. 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.
It is the mean one expects to observe if the treatment has no effect whatsoever. Minimum Detectable Effect. The minimum effect of interest, which is often called the minimum detectable effect MDE , but more accurately: MRDE, minimum reliably detectable effect should be a difference one would not like to miss , if it existed.
It can be entered as a proportion e. For example, if the baseline mean is 10 and there is a superiority alternative hypothesis with a superiority margin of 1 and the minimum effect of interest relative to the baseline is 3, then enter an MDE of 2 , since the MDE plus the superiority margin will equal exactly 3. In this case the MDE MRDE is calculated relative to the baseline plus the superiority margin, as it is usually more intuitive to be interested in that value.
If entering means data, one needs to specify the mean under the null hypothesis worst-case scenario for a composite null and the standard deviation of the data for a known population or estimated from a sample. Type of alternative hypothesis. The calculator supports superiority , non-inferiority and equivalence alternative hypotheses. The equivalence margin cannot be zero. See Types of null and alternative hypothesis below for an in-depth explanation. Acceptable error rates.
For an in-depth explanation of power see What is statistical power below. The type I error rate is equivalent to the significance threshold if one is doing p-value calculations and to the confidence level if using confidence intervals. Assume a population proportion of 0. Refer to the table provided in the confidence level section for z scores of a range of confidence levels. Thus, for the case above, a sample size of at least people would be necessary.
Financial Fitness and Health Math Other. Confidence Level:. Margin of Error:. Population Proportion:. Sample Size Calculator. Updated July 24, Accessed January 13, All rights reserved. Home Academy Blog About. Back to Top. Group 1 The anticipated mean and standard deviation of group 1 eg, mmHg, 75 kg Standard deviation is determined by examining previous literature of a similar patient population.
Enrollment ratio The ratio of group 2 to group 1 enrollment. For most studies, the enrollment ratio is 1 ie, equal enrollment between both groups. Some studies will have different enrollment ratios , for additional safety data.
We take the time to compare our calculators' output to published results. Moreover, our computation code is open-source, mathematical formulas are given for each calculator, and we even provide R code for the adventurous.
The validation examples are cited at the bottom of each calculator's page. We are a group of analysts and researchers who design experiments, studies, and surveys on a regular basis.
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