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Some form of quality control is essential to ensure that those ascertaining the physical sign of visible flexural dermatitis are recording something valuable. Ideally quality control should examine both validity (comparison of your observer's responses to an external standard) and between and within observer variation. At the end of the day, practical considerations such as the number of observers, availability of reliable local validators and the nature of comparisons performed will determine the method of quality control most suitable for any one particular study.
We have provided a simple system for checking your observer's responses to the visible flexural dermatitis protocol by using a set of 30 test photographs (labelled "test photographs" as part of this manual). Please ask your observers to complete the online test by marking each photograph as either "yes" or "no" in the box provided. Systematic error and Mean Pair Agreement Index (see below) have been chosen as the main outcome measures. Ideally, quality control should be checked during the early field work of your survey so that problems can be rectified. If this is not possible, it would still be worthwhile conducting the quality control test on your observers at the end of the study so that you can explore the effects of possible misclassification.