Stone et al. (2003) compared the completion of a paper and electronic pain diary. The paper diary was fitted with a hidden device to track the opening and closing of the binder, to help monitor completion. It was found that on 32% of study days the paper diary was not opened, yet the compliance for these days was >90%. This suggests there has been backfilling of data, questioning the reliability of the data. This is further confirmed by Gaertner et al. (2004) who demonstrated more retrospective fabrication of data in the paper diary.