Mann-Kendall Trend Test and Sen’s Slope, in Your Browser
Paste or drop a monitoring series. You get the Mann-Kendall S statistic, the variance with the tie correction, the normal approximation and its p-value, Sen’s slope with a confidence interval, and a plain-English verdict line — with non-detects carried as censored values rather than silently dropped.
Your data
Drop a logger CSV here
HOBOware and Postlad exports are recognised automatically. It is read on this machine — nothing is uploaded.
Synthetic five-year quarterly TCE record from a single monitoring well, in µg/L, with the result-and-qualifier column layout of a laboratory EDD. The record declines into non-detects at two different reporting limits — 0.5 µg/L routinely, and 1 µg/L for one diluted sample — which is what makes the choice of non-detect method visible. Not measured data.
SVG is vector — scale it to any size in Illustrator, Inkscape or LaTeX without losing quality, and edit the type. Use it unless a journal insists on raster.
Options
Series
Which measurement to test for trend.
Non-detects
How values reported as “<0.5” enter the test. This changes the answer, and the method used is printed on the figure.
Test
Two-sided is the honest default unless the direction was specified before the data were seen. The one-sided value is half the two-sided one.
Only the wording of the verdict depends on this. The p-value is reported whatever it is set to.
Slope
Two-sided limits by Gilbert (1987) §16.5, computed from the same tie-corrected VAR(S) the test used.
A year here is 365.25 days and a month is a twelfth of one, so the three are exactly proportional.
Figure
All of that was worked out in this browser tab. Your file was not uploaded, and no request goes out while you work — open the network panel and watch, if you like.