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what's the use of standard score?
Message posted by carol (via 202.66.193.28) on February 22, 2001 at 8:23 PM (ET)
How useful & accurate is standard score in comparing students' performances?
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Re: what's the use of standard score?
Message posted by Bill (via 192.231.71.108) on February 23, 2001 at 11:17 AM (ET)
If a student scores 160 on a math test and 790 on a history test, did the student score better relative to others who took the tests on the history test?? We don't have enough information to answer the question. If we know the mean and standard deviation of the tests then we can better interpret the results but it will be cumbersome. If we convert the raw scores to standard scores, we can more readily interpret the scores. A standard score is defined as z=(x-x(bar))/sd. Assuming the math and history tests have a mean (sd) of 200(20) and 750 (50) then the standard scores (z in this case although there are others, e.g. T scores) for math and history are -2 and .8. These are standard deviation units below (-2) and above (.8) the mean. Thus the student scored 2 sd below the mean on math and .8 sd above the mean on history. Clearly the history score was better than the math score. Standard scores are helpful in this situation. I'm not sure how to answer the "accurate" part of your question.
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