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Comparison of the various grading methods in a normal distribution, including: standard deviations, cumulative percentages, percentile equivalents, z-scores, T-scores. In statistics, the standard score is the number of standard deviations by which the value of a raw score (i.e., an observed value or data point) is above or below the mean value of what is being observed or measured.
A scaled score is the result of some transformation(s) applied to the raw score, such as in relative grading. The purpose of scaled scores is to report scores for all examinees on a consistent scale. Suppose that a test has two forms, and one is more difficult than the other. It has been determined by equating that a score of 65% on form 1 is ...
The two columns to the right of the left-most column in this computerized table are raw data. Raw data, also known as primary data, are data (e.g., numbers, instrument readings, figures, etc.) collected from a source. In the context of examinations, the raw data might be described as a raw score (after test scores).
where z is the standard score or "z-score", i.e. z is how many standard deviations above the mean the raw score is (z is negative if the raw score is below the mean). The reason for the choice of the number 21.06 is to bring about the following result: If the scores are normally distributed (i.e. they follow the "bell-shaped curve") then
Percentile ranks are commonly used to clarify the interpretation of scores on standardized tests. For the test theory, the percentile rank of a raw score is interpreted as the percentage of examinees in the norm group who scored below the score of interest. [3] [4]
Then, the raw score is converted to a scaled score. As with the other tests, a scaled score of 2100 meets the standard and 2400 is a commended performance. In 2007, the 11th grade "met standard" level was a raw score of 42, 10th was 44, and 9th was 28; 7th "met standard" with 26 points and 4th with 20. [10]
Scores using this metric have historically been known as "raw" scores. Tests taken in October 2004 or later had a score range from 200 to 600. The median score was 400, with a standard deviation of 25 points. These scores, based on a normal curve, are known as "scaled" scores.
In the case of normalization of scores in educational assessment, there may be an intention to align distributions to a normal distribution. A different approach to normalization of probability distributions is quantile normalization , where the quantiles of the different measures are brought into alignment.