I often see epidemiological studies where a continuous variable has been divided into quantiles and the odds ratios for each quantile compared with a reference quantile are reported. In many of these studies the authors report a test for linear trend in the odds ratios, often termed a "P-trend." While most studies don't indicate what methods they used to determine this value, I've seen some studies create a new variable that is the median value of each quantile and use this variable in the regression to determine "P-trend." For example, the five level categorical variable would be (5 4 3 2 1) and the new variable would be (56.1 45.6 23.3 12.6 7.5). I haven't found any papers describing this method and so I'm not convinced it's appropriate, but I wanted to see if anyone else had come across this or could offer any input.