Page 225 - DEDU504_EDUCATIONAL_MEASUREMENT_AND_EVALUATION_ENGLISH

Unit 18 : Marking System : Need, Problems, Components

(b) Derived scores Based on Variability of Performance Notes
These are of two types :
(i) Percentile ranks, and
(ii) Scores that express position on a scale in units of standard deviation or quartile deviation.
(c) Derived scores Based on Standard Deviation
These may be of 4 types :
(i) Z scores
(ii) T score
(iii) Standard scores, scaled , equated scores and converted scores
(iv) Informal derived scores
• Calibration, Scaling and Equating
• Scaling is a technique that standardises raw scores or marks from one scale to another. Two
raw scores may be described equivalent and assigned the same degree of excellence in
relation to some relevant group.
• Two raw scores are defined as equivalent and all therefore are translated into the same
scaled score if they are at the same distance from the means of their distribution, in terms
ot standard deviations of their distribution, in terms of standard deviations of their
x – m
distribution, i.e. (x = score, m = mean, and S.D. = standard deviation).
S.D.
• Use of Linear or Normalised Method

• Linear-scale transformation produces a set of scores whose shape distribution is identical
with that of the raw scores, whereas normalised scale transformations force a non-normal
distribution of raw scores into a normal distribution of scaled scores.

• Sometimes when we suspect that a particular group is not really a representative group, we
may prefer to have a population (not sample), e.g.
• This is called equating because the final grades or marks are based on this year’s statistics
and on past statistics also.
(a) Statistical equating
(b) Equating grades
(i) Some common tests like entrance examination, aggregate marks at previous level or
it can be a special ‘scaling’ or a Link Test (e.g. Aptitude test) have to be used.

(ii) For all entering examinees or students on the entrance test or scaling test, frequency
distribution should be made.
• There are other systems of marking having different purposes to serve, with their own
advantages and limitations, as expressed below.
(i) Multiple marks on various aspects of achievement can improve marking but cost more in
extra efforts and may not be worth the improvement expected.
(ii) The more the marks available in the system indicating different levels of achievement,
the more reliable the marks will be, but the usability of this system is limited.
(iii) System of pass-fail marks does not serve the functions that marks are supposed to do,
especially in finely graded marks.
(iv) Numerical marks lay emphasis as measurement and simplify calculations of grade-point
averages.

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