2010 NGMP Calculator

Software

GNS Science has made a free excel based spreadsheet for automatic statistical analysis of water quality data. This GIS tool is free to use for non-commercial applications.

Overview

Potential outliers are identified using a non-parametric method. The user can control outlier detection sensitivity and whether or not outliers are excluded from subsequent data analysis.

Distributional parameters (e.g. median, average, median absolute deviation, standard deviation, etc.) are calculated on a per-site and per-analyte basis, using a log-probability regression method valid for datasets in which up to 80% of results are below the detection limit.

Temporal trends in the dataset are identified on a per-site and per-analyte basis, using the Mann-Kendall test. The user can perform either a non-seasonal or a seasonal trend test. For seasonal trend tests, the year can be divided into up to 12 different seasons, and the user can control the Julian day on which the first season starts.

Trend magnitudes are quantified using Sen’s Slope Estimator and a linear regression method. Seasonality is assessed with the Kruskal-Wallis test. As in the previous version of the spreadsheet, the user can opt to divide the year into up to 12 different seasons, and the user can control the Julian day on which the first season starts.

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