A statistical approach: you are comparing two conditions (old system vs. new system) and have an idea about the direction of the effect (the new system is more efficient, resulting in faster times).
Can you make an estimate of the expected difference between the two conditions? What is the smallest difference you would not want to miss? It takes more measurements to detect a small difference. Look up 'effect size' and 'statistical power'. Are you planning to test both conditions on the same subjects or are you planning to use two separate groups? For between-subjects measurements there are other statistical tests than for within-subject measurements. If everyone performs faster with the new system (and you have been careful to control for learning effects and other artefacts) you have a strong indication that the new system is faster. But if you use two separate groups, there is a chance that (by pure chance) the faster users end up in one group and the slower users in the other. If you can clearly state your assumptions, determining the sample size is pretty easy to do with basic statistics. Marielle Winarto . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Posted from the new ixda.org http://www.ixda.org/discuss?post=31284 ________________________________________________________________ Welcome to the Interaction Design Association (IxDA)! To post to this list ....... [EMAIL PROTECTED] Unsubscribe ................ http://www.ixda.org/unsubscribe List Guidelines ............ http://www.ixda.org/guidelines List Help .................. http://www.ixda.org/help
