Technical Report - International Military Testing Association

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Distractor-test corralstions indicate revision is ctcessarp if they
exceed the correlation set at the HA level. Distractor proportions are
indicated for rtvirion if they fall outside a range fro66 a proportion
of .OS to a proportion of .25. A minimum proportion of .OS wnd elected
to provide that scm6 plausiboility exist in all distractore in order thut
a theoretical chaacS6 scort.of 25 is teuablt. A msxinarn proportion of
.25 wa6 btltcted becauat (1) all rc6pons6s, distractox and correct
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altemativts, would have s proportion of .25, if examinaao had no icnm- .
ledge regarding the item and (2) when the.p-values of correct alter- ’
native6 approach .25, chance rc6ponses tend to lovar item-tsot correlation6
(Gullford, 1956, p. 437). .
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Applied in conjunction, the above limits provide: (1) that :tem
p-values lrvy range ‘bstween .25 and .85 which ie rearonsble in view of
the desired man; (2) that the resultant test mssu is near the desired
valus; (3) that wximm item standard deviation8 art obtained rince
item p-values am msintainsd at andiaa values; and (4) that item p-valuer
trt within ranpr wherein item-tart correlations art higher since extrexe
or nonmedian p-valu66 for items tend to reduce item-test correlations.
To iIlu6trata how Ponda 2 works in regard to the item coding
proctdurtt, we can take th? txmple of ittw coded CX and HA:
Given 100 item6 with item-ttrt corrtlacions of .30 (the tX level
for larger NCS 8+6ples) and item standard deviation6 of4-9
.48
the test standard dfmfation would be:
Ix - 100(.30)(.48) - 14.4
With 100 item having itmn ta6t correlationa of .20 (the minimslly
for larger HGS ramplea) aud i-em standard deviation6 of
.48, the test standard deviation would be:
sx - 100 (.20)(.48) - 9 . 6
’ ; With item 6tleCttd or revised to txcttd there item-test correlation6 and
to � pprosch these item standard dsvistions it in apparent that a daairtd
test standard deviation is tmdt more posriblt.
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‘lb illustrate how ?oxw~la 3 worka in relation to tbt item coding
procrdurtr,wt can use 100 items with the average variance of (.625)
(.357) - .23 and a test standard dwiation of 12.5. The miniatum tt6t
reliabflity in thir cast would be:
rxx - loo
99
l-.=&-.86
In this msnner adequate reliability tends to be iasursd by the item coding
procedure6 .
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