Roy Powell makes several points in his letter. We will attempt to be brief in our response.
We were aware of the papers he mentions, but the PAIS and the DISQ are different to the IPQ. We found one paper that evaluated the IPQ in a UK sample. We criticised that paper for failing to report the reliability and validity of the IPQ.1 Powell essentially confirms our four main criticisms of this paper:
He confirms that the reliability of the IPQ was not reported, a surprising error in a paper that claims to establish the reliability of the IPQ.
The researchers combined two measures. They then disaggregated them using principal components analysis. This circular logic says nothing about the reliability and validity of the IPQ.
Older patients had higher scores on the IPQ, but there was no evidence that they were more satisfied. The conclusion that this confirms the validity of the IPQ is, once again, circular. This also applies to the other papers cited here.
He suggests that the item-total correlation of r = 0.78 validates the IPQ against the criterion of item 27 of the IPQ. He has this the wrong way around: the item-total correlation validates item 27 against the criterion of the IPQ. In neither case is the IPQ validated against a meaningful criterion.
We have commented on the relevance of the expert panel to this debate.2 Our review was restricted to peer-reviewed publications. If the independent experts had access to additional data, then perhaps these should be published to allow researchers and other interested parties equal access to the relevant material
We do not agree that we should have approached the IPQ research team before publishing our critical review. We found no peer-reviewed evidence that the QOF patient surveys were valid and reliable and our results have been available since we presented them at conference in 2006.3 No further relevant data were forthcoming from the IPQ team.
Far from being a ‘complete rebuttal’, we feel that Powell's comments fully support our findings, and we are pleased to find these issues discussed in a public forum.
- © British Journal of General Practice, 2008.