Cohen's Adjustment

 

See Also:

Transforming Data

Aitchison's Adjustment

 

Description:

 

Cohenadjust provides a technique to better accommodate non-detect (or censored) values in some statistical methods.

 

Use:

 

ChemStat uses Cohenadjustment to calculate an adjusted mean and standard deviation. These adjusted parameters are calculated for each monitoring location individually, for all background monitoring locations as a group, and for all monitoring locations (compliance and background) as a group. Monitoring locations classified as "unused" are not included in the calculations.

 

Once Cohenadjustment has been selected, the adjusted means and standard deviations will be used in all calculations that require a mean and standard deviation (i.e., methods such as Kruskal-Wallis would not be affected).

 

Important considerations in using this method:

  • Once selected, all statistical methods that require a mean or standard deviation will use the adjusted mean and standard deviation.
  • Non-detects are represented by the full detection limit when appropriate.
  • It is possible, and may often be desirable, to apply Cohenadjustment to transformed data.