It sounds like he's working with IQ test data which is normed to a mean of 100 and SD of 15. If that is the case, he should first check that his sample's variance is not different from the norm for the test, then use a Z test. If it is different, use t-test.
Of course, if the sample is big enough we are just arguing a distinction without a difference. Paul Jay Warner said on 10/5/02 11:05 PM: >May I ask, how you _know_ that the stdev = 15? Did you set it this way? >Do you >have lots of data to show it so? > >I'd like to suggest that you can only _estimate_ stdev from "external" or >"internal" data. the former is when it comes from elsewhere, the latter >when it >comes from the data under analysis. In the former case we have no way of >establishing the confidence of the estimate, so we take it as "known" and >use a >z test. > >However you 'normalize' your data, it looks to me that you are estimating the >stdev from the data under review - thus, an internal estimate. > >If so, then you will wind up with a t test. > >If you choose to compare a data sample against a 'norm' then you have a >one-sample test. > >Thus, a one sample t test. QED. > >If you normalize your data to reach a mean of 100 and a stdev of 15, are >you not >'giving away' some information? I believe a recent post here advised against >excessive 'normalizing' and other manipulations of the data not related to >the >nature of what was being measured - the technology. Whether or not your >situation qualifies as 'excessive' only a knowledge expert can tell, I >believe. > >Cheers, >Jay > >Christopher Larsen wrote: > >> I am looking at doing an analysis of some data on memory performance on a >> standardized test of recall memory. The norms on each scale of the test are >> 100 with a standard deviation of 15. I am wanting to compare my data set to >> the normative data. Which would be a superior test to use, a Z test or a >> One Sample T-Test??? . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . =================================================================
