Table 6 Results of the assessment of DIF for each of the 9 remaining items of the brief MHQ, across each person variable. DIF was assessed in three ways: ANOVA, visual inspection of the DIF graphs and by inspecting the mean scores across the class intervals

How was the sensation (feeling) in your hand(s) during the past week?

Treatment choice

0.0005

Uniform DIF

Mean differences between categories are relatively even across class intervals

How difficult was it for you to hold a frying pan during the last week?

Sex

0.0003

Non-uniform DIF (DIF graph lines intersect)

Mean differences between categories are uneven across class intervals

How difficult was it for you to button a shirt or blouse during the past week?

Sex

0.0008

Uniform DIF

Mean differences between categories are relatively even across class intervals

How often were you unable to do your work in the past week because of problems with your hand(s)?

PCS

0.001

Non-uniform DIF (DIF graph lines intersect)

Mean differences between categories are uneven across class intervals

Describe the pain in your hand(s)/wrist(s) in the past week?

PCS

 < 0.0001

Non-uniform DIF (DIF graph lines intersect)

Mean differences between categories are uneven across class intervals

IPS

 < 0.0001

Non-uniform DIF (DIF graph lines intersect)

Mean differences between categories are uneven across class intervals

Treatment choice

 < 0.0001

Non-uniform DIF

Mean differences between categories are uneven across class intervals

How often did the pain in your hand(s)/wrist(s) interfere with your daily activities (such as eating or bathing)?

Treatment choice

0.0003

Non-uniform DIF (DIF graph lines intersect)

Mean differences between categories are uneven across class intervals

In the past week, how satisfied are you with the motion of your fingers?

Treatment choice

0.001

Uniform DIF

Mean differences between categories are uneven across class intervals