Figure 2 .

Physical functioning item calibrations for the Dutch WOMAC and the English WOMAC. English calibrations on the x axis, and Dutch on the y axis. Calibrations are expressed in logits. Negative calibrations indicate easier items. Positive calibrations indicate more difficult items. An identity line is drawn through the origin, with a slope of 1. Statistical control lines (95% CI) are drawn around the identity line (dotted lines). The area between the dotted lines depicts acceptable item deviation. Items outside the control lines demonstrate DIF. The numbers near the data points refer to the WOMAC item numbers. For a full explanation of the items see table 1.