Comparison of means (t-test)

Command:

Tests Comparison of means (t-test)

Description

Performs a t-test for the comparison of the means of two independent samples.

This test is not performed on data in the spreadsheet, but on statistics you enter in a dialog box.

Required input

The program displays the difference between the two means, and a 95% confidence interval for this difference. Next, the P value is displayed: when this P value is less than 0.05, the conclusion is that the two means are significantly different.

In the example, the mean 256 (standard deviation 22 and sample size 50) of the first sample, is compared with the mean 232 (standard deviation 32 and sample size 50) of the second sample. The difference between the two means is 24. The 95% confidence interval for this difference ranges from 13.1 to 34.9 (note that this interval excludes the value 0). The hypothesis test results in a P-value less than 0.0001, and the conclusion therefore is that, statistically, there is a significant difference between the two means.

In the Comment input field you can enter a comment or conclusion that will be included on the printed report.

Literature

• Bland M (2000) An introduction to medical statistics, 3^rd ed. Oxford: Oxford University Press.

Recommended book

An Introduction to Medical Statistics
Martin Bland

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This textbook is intended for medical researchers and includes the design of clinical trials and epidemiological studies, data collection, summarizing and presenting data, probability, standard error, confidence intervals and significance tests, techniques of data analysis including multifactorial methods and the choice of statistical method, problems of medical measurement and diagnosis, vital statistics, and calculation of sample size.