I have a distribution of values for each of 12 months. When I draw the boxplots (one boxplot for each month) the median gradually increases, but the boxes overlap.
Which test do I have to use in order to tell whether this seeming increase is significant or not? Also, how would I quantify the increase? e.g. if between January and Feb the median increased by 1, but the box plots for these two months largely overlap, is that even meaningful?