On the variability of trend test results

Abstract

Trend tests are used to investigate statistical significance of trends. The popular Mann–Kendall (MK) trend test was originally proposed for random data. It was later modified to handle correlated data. After the scaling hypothesis was introduced, the MK test was further modified to accommodate it. The results from these three versions of the MK test can be very different. The objective of the present paper is to illustrate these variations in the MK trend test results. Not considering these variations would lead to spurious conclusions about statistical significance of trends in data with associated erroneous deductions. Monthly temperature data from Malaysia are used for illustration.