One sample t-test

Command:

Statistics T-tests One sample t-test

Description

Use the one sample t-test to test whether the average of observations differs significantly from a test value.

Required input

• The variable of interest. You can use the button to select variables and selection criteria in the variables list.

• The test value you want to compare the sample data with.

Options

Logarithmic transformation: if the data require a logarithmic transformation (e.g. when the data are positively skewed), select the Logarithmic transformation option.

Results

The results window first displays the summary statistics of the observations.

The One sample t-test panel shows:

• The test value
• The difference Sample mean - Test value
• The 95% Confidence Interval (CI) for this difference
• The Degrees of Freedom (DF), t-statistic, and corresponding (two-sided) P-value.

If the calculated P-value is less than 0.05, the conclusion is that, statistically, the sample mean is significantly different from the test value.

Log transformation

If you selected the Log transformation option, the program performs the calculations on the logarithms of the observations, but reports the back-transformed summary statistics.

For the One sample t-test, the difference between sample mean and test value, with 95% confidence interval, are given on the log-transformed scale.

Next, the results are transformed back and the interpretation is as follows: the back-transformed difference of the logs is ratio of the sample mean / test value on the original scale.

Literature

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

See also

• Independent samples t-test
• Paired samples t-test