*LAB
Session on item analysis.*
(Reliability:
Dichotomous data (psychology.test)
RELIABILITY
/VARIABLES=q1
q2 q3 q4 q5 q6 q7 q8 q9 q10 q11 q12 q13 q14 q15 q16 q17 q18
q19 q20 q21
q22 q23 q24 q25 q26 q27 q28 q29 q30 q31 q32 q33 q34 q35 q36 q37
q38 q39 q40
q41 q42 q43 q44 q45 q46 q47 q48 q49 q50
/FORMAT=NOLABELS
/SCALE(ALPHA)=ALL/MODEL=ALPHA
/STATISTICS=DESCRIPTIVE SCALE CORR
/SUMMARY=TOTAL MEANS VARIANCE .
*Computing
a composite score to compute
item-total correlation*
COMPUTE sum2 = q2+
q3+q4+q5+q6+q7+q8+q9+q10+q11+q12+q13+q14+q15+q16+q17+q18+
q19+q20+q21+q22+q23+q24+q25+q26+q27+q28+q29+q30+q31+q32+q33+q34+q35+q36+q37+
q38+q39+q40+q41+q42+q43+q44+q45+q46+q47+q48+q49+q50.
EXECUTE .
CORRELATIONS
/VARIABLES=q1 sum2
/PRINT=TWOTAIL NOSIG
/MISSING=PAIRWISE .
*Cross
validation*
*Create a
filter. Turn the filter off.
Run reliability for both groups.*
USE ALL.
COMPUTE
filter_$=(uniform(1)<=.30).
VARIABLE
LABEL filter_$ 'Approximately 30 % of cases (SAMPLE)'.
FORMAT
filter_$ (f1.0).
FILTER BY
filter_$.
EXECUTE .
FILTER
OFF.
USE ALL.
EXECUTE .
SORT CASES
BY filter_$ .
SPLIT FILE
SEPARATE BY filter_$ .
RELIABILITY
/VARIABLES=q1
q2 q3 q4 q5 q6 q7 q8 q9 q10 q11 q12 q13 q14 q15 q16 q17 q18
q19 q20 q21
q22 q23 q24 q25 q26 q27 q28 q29 q30 q31 q32 q33 q34 q35 q36 q37
q38 q39 q40
q41 q42 q43 q44 q45 q46 q47 q48 q49 q50
/FORMAT=NOLABELS
/SCALE(ALPHA)=ALL/MODEL=ALPHA
/STATISTICS=DESCRIPTIVE
/SUMMARY=MEANS VARIANCE .
*Reliability:
Polytomous data set (agg.sav): Criterion reference*
RELIABILITY
/VARIABLES=i1 i2 i3 i4 i5 i6 i7 i8 i9 i10 i11 i12 i13
/FORMAT=NOLABELS
/SCALE(ALPHA)=ALL/MODEL=ALPHA
/STATISTICS=DESCRIPTIVE SCALE CORR
/SUMMARY=TOTAL MEANS VARIANCE .
*Reliability:
Polytomous data set (agg.dat) without item 12*
RELIABILITY
/VARIABLES=i1 i2 i3 i4 i5 i6 i7 i8 i9 i10 i11 i13
/FORMAT=NOLABELS
/SCALE(ALPHA)=ALL/MODEL=ALPHA
/SUMMARY=TOTAL MEANS VARIANCE .
*Computing
a composite score to compute item-total correlation*
COMPUTE
sum= i2 + i3 + i4 + i5 + i6 + i7 + i8 + i9 + i10 + i11 +
i13 .
EXECUTE .
CORRELATIONS
/VARIABLES=sum i1
/PRINT=TWOTAIL NOSIG
/MISSING=PAIRWISE .
*Computing
a composite score *
COMPUTE
composit= i1 + i2 + i3 + i4 + i5 + i6 + i7 + i8 + i9 + i10 + i11 + i12
i13 .
EXECUTE .
*mean and
variance of individual items*
FREQUENCIES
VARIABLES=i1 i2 i3 i4 i5 i6 i7 i8 i9 i10 i11 i12 i13
/STATISTICS=VARIANCE MEAN
/ORDER ANALYSIS .