Table 3. Item parameters and standard errors (SE) for anchor and study items used in the analysis of differential item functioning on the DASS-21 for male and female medical students using GRM
Items Group a(SE) b1(SE) b2(SE) b3(SE) Test for DIF
Non-uniform c2(df), p Uniform c2(df), p
Depression            
  1.      I couldn't seem to experience any positive   feeling at all Male Female 1.69(0.19) 1.69(0.19) -0.04(0.10) -0.04(0.10) 1.53(0.15) 1.53(0.15) 2.59(0.25) 2.59(0.25) Anchor
  2.      I found it difficult to work up the initiative to  do things Male Female 0.71(0.15) 1.09(0.19) -1.25(0.32) -0.52(0.19) 2.08(0.46) 2.10(0.32) 4.44(0.96) 4.23(0.70) 2.5(1), 0.118 7.3(3), 0.063
  3.      I felt that I had nothing to look forward to Male Female 3.73(0.50) 3.73(0.50) 0.44(0.08) 0.44(0.08) 1.57(0.13) 1.57(0.13) 2.30(0.20) 2.30(0.20) Anchor
  4.      I felt down-hearted and blue Male Female 2.63(0.29) 2.63(0.29) -0.22(0.09) -0.22(0.09) 1.33(0.12) 1.33(0.12) 2.51(0.22) 2.51(0.22) Anchor
  5.      I was unable to become enthusiastic about  anything Male Female 1.94(0.22) 1.94(0.22) 0.38(0.09) 0.38(0.09) 1.95(0.18) 1.95(0.18) 2.96(0.29) 2.96(0.29) Anchor
  6.      I felt I wasn't worth much as a person Male Female 2.24(0.26) 2.24(0.26) 0.63(0.10) 0.63(0.10) 1.86(0.17) 1.86(0.17) 3.04(0.30) 3.04(0.30) Anchor
  7.      I felt that life was meaningless Male Female 2.42(0.28) 2.42(0.28) 0.43(0.09) 0.43(0.09) 1.59(0.15) 1.59(0.15) 2.47(0.22) 2.47(0.22) Anchor
Anxiety            
  1.      I was aware of dryness of my mouth Male Female 0.67(0.18) 0.73(0.15) 0.66(0.25) 0.37(0.21) 3.61(0.92) 3.79(0.72) 7.45(2.16) 6.52(1.40) 0.1(1), 0.785 3.0(3), 0.398
  2.      I experienced breathing difficulty Male Female 1.26(0.21) 1.54.(0.33) -1.09(0.20) -1.09(0.27) 1.44(0.23) 0.70(0.25) 2.96(0.45) 2.47(0.57) 0(1), 0.85 0.6(3), 0.90
  3.      I experienced trembling (e.g., in the hands) Male Female 0.97(0.20) 1.15(0.19) 0.35(0.15) 0.53(0.16) 2.18(0.39) 2.58(0.36) 3.55(0.67) 4.41(0.68) 0.4(1), 0.532 7.0(3), 0.073
  4.      I was worried about situations in which I might   panic and make a fool of myself Male Female 1.26(0.22) 1.21(0.19) -0.23(0.13) -0.06(0.15) 1.65(0.25) 2.00(0.27) 3.02(0.48) 3.71(0.52) 0.0(1), 0.864 2.6(3), 0.453
  5.      I felt I was close to panic Male Female 2.09(0.37) 2.48(0.45) 0.67 (0.11) 0.50(0.11) 2.00(0.24) 1.84(0.19) 3.58(0.66) 2.91(0.34) 0.4(1), 0.503 1.4(3), 0.699
  6.      I was aware of the action of my heart in the absence of physical exertion Male Female 0.84(0.17) 2.00(0.42) -0.55(0.21) -0.83(0.23) 2.18(0.42) 1.02(0.28) 3.88(0.76) 2.20(0.50) 0.2(1), 0.66 3.6(3), 0.31
  7.      I felt that life was meaningless Male Female 2.11(0.39) 1.91(0.33) 0.84(0.12) 0.75(0.12) 2.06(0.25) 2.15(0.23) 2.83(0.40) 3.08(0.37) 0.2(1) 0.696 0.7(3) 0.882
Stress            
  1.     I found it hard to wind down Male Female 0.58(0.12) 0.58(0.12) 0.66(0.23) 0.66(0.23) 4.96(1.03) 4.96(1.03) 8.04(1.78) 8.04(1.78) Anchor
  2.     I tended to over-react to situations Male Female 1.40(0.28) 1.33(0.23) 1.20(0.19) 1.13(0.18) 2.81(0.46) 2.88(0.38) 4.57(1.06) 4.28(0.66) 0.5(1), 0.47 6.3(3), 0.099
  3.     I felt that I was using a lot of nervous energy Male Female 1.37(0.21) 1.37(0.21) -0.89(0.18) -0.89(0.18) 0.87(0.17) 0.87(0.17) 2.44(0.36) 2.44(0.36) Anchor
  4.     I found myself getting agitated Male Female 2.30(0.42) 2.73(0.56) -0.26(0.11) -0.65(0.20) 1.44(0.16) 0.99(0.27) 2.45(0.29) 2.29(0.49) 0.4(1), 0.536 5.2(3), 0.15
  5.     I found it difficult to relax Male Female 2.22(0.40) 2.35(0.49) -0.10(0.11) -0.61(0.20) 1.52(0.17) 1.27(0.32) 2.69(0.33) 2.11(0.47) 0.0(1), 0.834 7.6(3), 0.054
  6.     I was intolerant of anything that kept me from getting on with what I was doing Male Female 0.84(0.17) 2.00(0.42) -0.55(0.21) -0.83(0.23) 2.18(0.42) 1.02(0.28) 3.88(0.76) 2.20(0.50) 6.5(1), 0.011 10.9(3), 0.012
  7.     I felt that I was rather touchy Male Female 1.28(0.21) 1.98(0.42) -0.85(0.18) -1.13(0.26) 1.29(0.20) 0.45(0.21) 3.32(0.50) 1.95(0.45) 2.2(1), 0.139 6.2(3), 0.102
Int J Med Educ. 2017; 8:116-122; doi: 10.5116/ijme.58ba.7d8b