QuickTTest - a programme for carrying out Student's t-test Version 1.3
Many scientists make frequent use of Student's t-test for assessing the significance of differences and all statistical packages contain routines to calculate this statistic. However, in my experience these programmes always require you to enter the individual data values. Not infrequently one would like to be able to calculate the t-values from already known mean ± SEM or mean ± SD values and this is not usually possible with existing programmes. I wrote this programme to provide such a functionality.
The programme is simple to use. The default data mode entry is for individual values which are entered in the QuickTTest window which opens at the upper left of the screen. A running total of mean, SEM, SD and number of values (n) is maintained in this window. When all the values for a group are entered, the Store button should be clicked to store the values for that group in the Data Summary window in the upper right of the screen. When at least two groups have been stored, the t-test button can be clicked which opens a further window at the bottom left of the screen. Here you can select which two groups you wish to carry out the t-test on. Clicking the Calculate button carries out the t-test. Clicking the More data button closes this window and returns you to data entry mode where you can enter further groups of data.
At any stage, the method of data entry can be changed by selecting from the Options menu either SEM entry or SD entry. Selection of either of these options brings up a further window at the bottom right of the screen. Here you can enter 'Mean', 'SEM' (or 'SD'), and 'n' for the two groups to be tested. Tabbing takes you from one data entry box to the next. When all data for the two groups are entered the Calculate button can be clicked to perform a t-test on the data. Any of the data values can be changed in order to carry out another t-test. To return to entry of individual data values, select Data entry from the Options menu.
When data have been entered it is possible to print the data values together with the results of t-tests using Print from the File menu. You can also save the data and results in a TEXT file by selecting Save as text.. from the File menu. This file can then be opened by any word-processing programme so it can be formatted as you wish. Note that only data entered as individual values in the QuickTTest window and the t-test results based on these values can be Saved or Printed.
That's about it. This is freeware. If anyone tries the programme and finds it useful, I'd be pleased to receive an email or postcard. Suggestions for improvement are encouraged. Any bug reports would also be welcomed - so far I have had no problems running under Systems 7.5.1 to 8.6
Acknowledgements
I am indebted to Paul England for the empirical equations that QuickTTest uses to approximate the t-distribution. I also want to thank all those users of the first version who emailed me with comments and suggestions. The most frequent requests were for 'Saving' and 'Printing' functionality and this is included in this version. Other improvements will be incorporated in future versions.
Version history
First release - Nov 1995
Version 1.1 - April 1996. Now incorporates the ability to Print or Save data and t-test calculations
Version 1.2 - April 1997. Corrected a mistake in the calculation of 't' under conditions where the approximate t-test has to be used (samples of very different variance)
Version 1.3 - October 1999. Can now return to entering individual values via the Options menu, even if the QuickTTest and/or Data Summary window(s) have been closed.
