z-Score Computation

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z-Score Computation

Post by rogerwimmer » Sun Dec 12, 2010 4:55 am

Dr. Wimmer: I just got back my AMT results in an Excel file. They're scored on a 0 to 100 scale. I'd like to see them as z-scores instead. Is there something I can do in Excel to convert them? If so, please instruct me if you are willing. Thanks! - Anonymous

Anon: As I have said many times, z-scores are probably the most useful statistic in behavioral research because they allow for "apples-to-oranges" comparisons. The procedure for computing z-scores is simple.

But before you get started, if you used a research company to conduct your music test, ask someone there to compute z-scores for you. The research company should be able to do that for you in just a few minutes. If you didn't use a research company, then here is what you need:

1. Calculate the Mean for all the scores in your data set (songs in your case).

2. Calculate the Standard Deviation for all the scores in your data set.

3. Calculate a z-score for each item (song) using this simple formula:

z = (Song – Mean) / Standard Deviation

(That's . . . Song minus the Mean divided by the Standard Deviation)

For more information, here is a quick summary of z-scores, and here is an Excel example for you.

I think that should help you, but let me know if you have problems. I'll figure out another alternative for you.

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Roger Wimmer is owner of Wimmer Research and senior author of Mass Media Research: An Introduction, 10th Edition.

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