Response bias? The graph I plotted SF36 scores against 6MWT scores to see if that would throw some light on response bias. If response bias happens, you would expect to see this at the end of the trial (52 weeks), when factors like wanting to support the therapist/doctor come into play but not at baseline, when particpants don't even know which therapy they will get. The graph shows a pretty consistent relationship between SF36 scores and 6MWT scores at baseline, shown by the blue trend line (and red squares). At 52 weeks there isn't such a clear pattern (green triangles), but the SF36 scores are higher than you would predict given the relationship between SF36 and 6MWT at baseline. It's as if the SF36 scores have been boosted a little - which could be the response bias. - WSAS is data for the 4 quartiles given in the Cella paper, using PACE baseline data for the Work and Social Adjustment Scale. It's the same basic data as PACE baseline, but chopped up a different way. Nb all these data points are group means (each group is around 150 people), not data for individual participants. This is all speculation though and comments welcome. ps happy to supply excel file with data and graph if anyone wants it.