Ψlogical Testing

Test-retest

different test, same occasion¹
aka sampling from the same domain elements
- similarly representative of construct
items should be of same difficulty level

…which are “parallel” to Form A and
which are not?

Form	Item 1	Item 2	Item 3	Item 4
A	\(2+3=?\)	\(9\div3=?\)	\(4\times5=?\)	\(4-1=?\)
B	\(1+4=?\)	\(6-3=?\)	\(2\times3=?\)	\(8\div4=?\)
C	\(-3+1.5=?\)	\(7\div13=?\)	\(.13\times\frac{5}{6}=?\)	\(-9-6=?\)
D	\(4+3=?\)	\(5+2=?\)	\(6+1=?\)	\(2+4=?\)

same test, same occasion
treat as though 2 different tests
must apply correction because of artificial halving
- Spearman-Brown prophecy formula
- what reliability would have been if you hadn’t chopped test in two

same test, same occasion
both indices of internal consistency
- cohesion of item response within scale
- scale needs at least 3 items
KR₂₀ used with tests
\(\alpha\) used with inventories

aka inter-rater reliability
do judges tend to agree (e.g., who is best, worst, etc)
- sometimes uses correlation coefficient
- sometimes uses other index (e.g., Kappa)

For MOST, index expressed as correlation
For ALL:
- larger = greater reliability
- capped at value of 1.0
- typically¹ never expressed as negative value

Standard error of measurement
- used to construct score bands
- same concept as within political polling
  - True value thought to be within band (with, e.g., 95% certainty)

Cronbach, L. J. (1951). Coefficient alpha and the internal structure of tests. Psychometrika, 16(3), 297–334.

Kuder, G. F., & Richardson, M. W. (1937). The theory of the estimation of test reliability. Psychometrika, 2(3), 151–160.

Spearman, C. (1904). The proof and measurement of association between two things. The American Journal of Psychology, 15(1), 72–101.

Thorndike, E. L. (1904). Theory of mental and social measurements. The Science Press.