This calculator runs the three standard t-tests used to compare two sets of sample data and decide whether the difference between their means is statistically meaningful, the same three tests found in the Excel Data Analysis Toolpak. You enter your figures into the Data 1 and Data 2 boxes, one value per line, and the results update automatically and appear side by side in three tables: Paired Two-Sample for Means, for matched or repeated measurements, which needs equal-sized data sets, Two-Sample Assuming Unequal Variances (Welch's t-test), and Two-Sample Assuming Equal Variances, a pooled-variance test. Each table shows the mean, variance and number of observations for both variables, plus the degrees of freedom, the t Stat, and the one-tail and two-tail p-values and critical t-values, so you can see straightaway whether your result clears the common 0.05 significance level. The paired test also reports the Pearson correlation between the two data sets, and the equal-variances test reports the pooled variance used in its workings. Use the Reset button to clear both boxes and start again. This suits students, researchers and anyone checking survey, experiment or before-and-after results for a genuine difference rather than random variation. As with any statistical test, the result is only as reliable as the data you enter, so check your sample sizes and assumptions before drawing conclusions from the output.
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