Science & Research Volume III - 4.11 Statistics Applied to pH in
Canned Foods Section 4 - Basic Statistics and Presentation
|EFFECTIVE DATE: 10/01/2003||REVISED: 01-31-13| pH is a
logarithmic measure for the acidity of an aqueous solution.
Since pH represents the negative logarithm of a number, it is
not mathematically correct to calculate simple averages or other
summary statistics. Instead, the values should be converted to
hydrogen ion concentrations, averaged, and re-converted to pH
values. The following guidance is provided - 1. Convert each pH
value to hydrogen-ion activity (H+), using the equation:
Activity = 10-pH In Excel, the formula is: =10^(-pH number) - 2.
Calculate the mean of the activity values by adding the values
and dividing the sum by the total number of values. Calculate
the standard deviation also from the activity values. - 3.
Convert the calculated mean activity back to pH units, using the
equation: pH = (-)(log10)(mean H+ activity). Also convert the
standard deviation to pH units. In