Frequent Questions

How do I calculate the 90th Percentile for Lead and/or Copper?

CALCULATING THE 90TH PERCENTILE FOR LEAD AND COPPER

If you collect 5 samples... rank the results from the lowest to the highest value, and then average the two highest results. This value is the 90th percentile.

If you collect 10 samples... rank the results from the lowest to the highest value, numbering each from 1 to 10. The 9th value is the 90th percentile.

If you collect 20 or more rank the results from the lowest to the highest value, numbering each from 1 up samples... to the number of samples taken. Multiply the number of samples taken by 0.9. The resulting number is the value that is the 90th percentile.

Example calculation: 20 samples x 0.9 = 18. The 18th value in a ranked set of sample values is the 90th percentile.

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