title: Eyes or patients? Traps for the unwary in the statistical analysis of ophthalmological studies.
abstract: In reports on ophthalmological research the results of measurements on the eye are often expressed as mean and standard deviation based on m patients, n eyes (n greater than m). This approach leads to t tests that are invalid because the measurements on the two eyes of one subject are usually related, not independent. In a simulation study involving intraocular pressure data analysed in this way, the null hypothesis of no difference between groups was rejected at a nominal alpha = 0.05 level in 39 out of 200 simulations; thus the true alpha was nearly 0.2. This approach is excessively prone to produce false positive results.
authors: Department of Medical Computing and Statistics, University of Wales College of Medicine, Cardiff.
authors: R G
authors: RG
authors: Newcombe
authors: G R
authors: GR
authors: Duff
mesh_terms: D003627:Data Interpretation, Statistical; D005189:False Positive Reactions; D006801:Humans; D007429:Intraocular Pressure / Q000187:drug effects*; D009248:Nadolol / Q000494:pharmacology; D011897:Random Allocation; D013999:Timolol / Q000494:pharmacology
chemical_list: D009248:Nadolol; D013999:Timolol