Page 172 - DEDU504_EDUCATIONAL_MEASUREMENT_AND_EVALUATION_ENGLISH

Educational Measurement and Evaluation

Notes 60th percentile” means that the individual’s score is the same as or higher than the scores of 60%
of those who took the test. The 50th percentile is known as the median and represents the middle
score of the distribution.

Percentiles have the disadvantage that they are not equal units of measurement. For
instance, a difference of 5 percentile points between two individual’s scores will have
a different meaning depending on its position on the percentile scale, as the scale tends
to exaggerate differences near e mean and collapse differences at the extremes.

Percentiles can not be averaged nor treated in any other way mathematically. However they do
have the advantage of being easily understood and can be very useful when giving feedback to
candidates or reporting results to managers.
If you know your percentile score then you know how it compares with others in the norm
group. For example, if you scored at the 70th percentile, then this means that you scored the same
or better than 70% of the individuals in the norm group.
This is the score most often used by organizations when comparing your score with that of other
candidates because they are so easily understood they are very widely used when reporting
results to managers.
The characteristic way that test scores tend to bunch up around the average and the use of
percentiles in the interpretation of test results, has important implications for you as a job
candidate. This is because most aptitude tests have relatively few questions and most of the
scores are clustered around the mean. The effect of this is that a very small improvement in your
actual score will make a very substantial difference to your percentile score.
To illustrate this point, consider a typical aptitude test consisting of 50 questions. Most of the
candidates, who are a fairly similar group in terms of their educational background and
achievements, will score around 40. Some will score a few less and some a few more. It is very
unlikely that any of them will score less than 35 or more than 45. Looking at these results in
terms of percentiles is a very poor way of analyzing them and no experienced statistician would
ever use percentiles on this type of data. However, nine times out of ten this is exactly what
happens to these test results and a difference of three or four extra marks can take you from the
30th to the 70th percentile. This is why preparing for these test is so worthwhile as even small
improvements in your results can make you appear far superior candidate.

What are transformed scores ?

Self Assessment
(i) A raw score is on original datum that has not been transformed.
X– M
(ii) The formula for Converting raw scores into Z-scores is Z =
σ
(iii) The formula for Converting raw scores into T-scores is T = 5 + 10Z
(iv) The formula for Converting raw scores into C-scores is C = 5 + 2Z
(v) The Stanine scores are better them C-scores from analysis viewpoint .
(vi) The meaning of more than + 2Z score is Good.
(vii) A percentile score is not the other type of Converted score.

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