QuickTTest - a programme for carrying out Student's t-test
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 requires 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 futher 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.
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. If there is sufficient interest I might be stirred into adding more functionality, in particular the ability to Save and Print the data and calculation results. Any bug reports would also be welcomed - so far I have had no problems running under System 7.5.1.
