So for these studies it is necessary and appropriate to calculate means based on the hydrogen ion concentrations. However, studies of surface water quality usually have another purpose. Surface waters contain buffers, and thus hydrogen ions do not behave conservatively and loadings cannot be logically calculated. Instead, the purpose of surface water studies is usually to summarize the central tendency of a population of lakes, provide descriptive statistics, and possibly conduct statistical tests to see if one population differs from another. If the researchers in these studies use parametric statistics such as means, standard deviations, and t-tests, they should be careful not to violate the assumptions on which such tests are based.
Parametric statistics assume a normal distribution of data.
In most cases, surface water acidity data are more nearly normal when expressed as pH rather than as hydrogen ion. If, however, we use the antilog method, we calculate a mean pH of 4.99, which does not appear central at all. A more serious problem arises when we attempt to calculate our confidence in the mean. Admittedly, most lake surveys won't find such an extreme range of pH values as shown in the hypothetical example in Table 1 . Still, typical lake surveys which use the antilog method to calculate means and standard deviations may be skewing their estimates of the central tendency and calculating misleading confidence intervals.