# Is "aggregate percentage" still a valid term in ecology?

Martin et al. 1946 define "aggregate percentage" as a metric that describes the mean percentage contribution of a group to the total mass/abundance of all samples. The metric is useful in datasets that are plagued by outliers and non-normality, something that is a commonplace with most ecological community and diet studies in my experience. Aggregate percentage is calculated as follows:

$AP_i = \frac{100\%}{N_y} \times \sum\limits_{j = 1}^{N}(\frac{a_{ij}}{\sum a_j})$

Where i is the i$^{th}$ taxon, j the j$^{th}$ sample, N total number of samples, a$_{ij}$ the abundance or mass of i$^{th}$ taxon in j$^{th}$ sample, and $\sum a_j$ the summed abundance or mass of all taxa in j$^{th}$ sample.

Martin et al. 1946 illustrate this as follows:

I am sure that "aggregate percentage" is a standard method in ecology, but I cannot find many studies using this term by googling. Probably the method has synonyms and there might be a more accepted term for the method nowadays. My question is what is the valid term to use for the method?

The formula of "aggregate percentage" that you show is just the arithmetic mean of percentages, and I suspect that no special term is used in most studies that use mean percentages as a measure of e.g. prey composition in a certain predator (as seems to be the case in your example).

When searching for studies I think you will have more luck with using "mean prey percentages", "prey percentages" or "mean percentage composition". For instance, see Shoup & Lane (2015) which includes the text (with my emphasis):

Results of regressions correlating Secchi depth (mm) with prey percentages by weight in the stomach contents of Largemouth Bass sampled from Boomer.

Also (Ahlbeck et al, 2012):

For each of the 25 individuals in each size class, the diet composition was calculated as the mass percentages of different prey, and then the average mass percentages were calculated for the size class.
[...]
prey percentages were first calculated for each fish separately and then averaged over all individuals in the sample (Hyslop 1980).

Finally, Ledger & Hildrew (2008):

Mean percentage composition (food category area as percentage total particle area) of faecal pellets of N. pictetii nymphs fed biofilm from four acid streams and four circumneutral streams.

• Thanks for clarification. It certainly seems that there is no standardized name for this method (which is just a mean of percentages, as you say). I suppose I was thinking about "frequency of occurrence", also a simple method that had several names until people settled to that term. I'll wait for some days and accept this answer unless someone comes up with a better one. Feb 26 '16 at 8:54
• @Mikko I agree that it's not entirely obvious, and people come up with all sorts of terms for basically the same thing (which can be a big problem). Personally, I hadn't heard of "aggregate percentage" before, and my main point is that most that use it as a statistic are probably not calling it that (or any other specific term necessarily). Feb 26 '16 at 10:01