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help for ^kr20^
by Herve M. CACI, August 1999 (v1.2)
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Kuder-Richardson coefficient of reliability
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     ^kr20^ varlist [^if^ exp][^in^ range], [sort(sortkey)]

Description
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Computes the reliability coefficient of a set of dichotomous items, whereas
Cronbach's alpha is used for multipoint scales.

In addition, ^kr20^ computes:
     - the item difficulty (proportion of 'right' answers),
     - the average value of item difficulty,
     - the item variance,
     - the corrected item-test point-biserial correlation coefficients,
     - the average value of corrected item-test correlation coefficients.

The items must be coded as: 
      - '0' for a wrong answer (unexpected answer),
      - '1' for a right answer (expected answer).

Global macros
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KR20 saves four results in the following global macros
      - $S_3: average value of item difficulties
      - $S_4: average value of corrected item-test PB correlation coefficients
      - $S_5: number of items
      - $S_6: KR20 

Options
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^sort(sortkey)^ to sort the output by 'item' name (alphabetically), or by
'DIFFiculty' level or 'CORRelation' coefficient.

Also see
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    STB:  ^alpha2^ in sg66 (STB-35)
 Manual:  ^[R] alpha^
On-line:  help for @factor@
