I am doing a DIF analysis for a test with polytomous items. My DIF analysis compared the item function between two years. My question is which part should I use to report the DIF?
I followed the tutorial and wrote these commands, containing two analyses as it said. I know the tutorial running this for comparing the step structure, but both would generate “TERM 3: item*year”. Should I report the “TERM 3: item*year” from the first model (item-year+item*year+year*item*step) or the one from second model (item-year+item*year+item*step)?
Here are my commands:
Title ASQSEBR DIF 36m;
datafile \Users\Tom Chen\Desktop\asqsebr_36m_dif.dat;
format responses 1-30 year 31;
set warnings=no;
codes 2,1,0;
model item-year+item*year+year*item*step;
labels << \Users\Tom Chen\Desktop\asqse_labels_36m.txt;
estimate ! iterations=10000,method=quadrature,nodes=15;
show!table=1:2 >>dif36m_a.shw;
reset;
datafile \Users\Tom Chen\Desktop\asqsebr_36m_dif.dat;
format responses 1-30 year 31;
set warnings=no;
codes 2,1,0;
model item-year+item*year+item*step;
labels << \Users\Tom Chen\Desktop\asqse_labels_36m.txt;
estimate ! iterations=10000,method=quadrature,nodes=15;
show!table=1:2 >>dif36m_b.shw;
