[Rasch] standardized scores

Anthony James luckyantonio2003 at yahoo.com
Mon Nov 28 01:30:59 EST 2011

Dear all,
In an introductory research and statistics book there’s a chapter on standard scores (z score and T score) and there are some activities at the end. One of the activities reads something like this:
There are two groups, one experimental and one control. After the treatment we give them different tests which have different scales for scoring. The scores of Group 1 are 3, 3, 5, 8, 9, 10, etc. and scores of Group 2 are 25, 87, 55, 78, 94, 36, etc. Has the treatment been effective?
I believe the author expects the students to convert the scores to z-scores or any other standard score and then compare the means of the standardized scores. Am I right?
Does transforming scores to z scores make scores across tests and groups comparable? Z scores are scores in standard deviation units and depend on the ability of the population. Can we compare two groups in this way?
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