I am looking for statistical methods used to compare frequency of observations between two groups. suppose I have two groups of pigeons with the same sample sizes, say 10. The number of red blood cells of any pigeon are counted. The observations are as follows:

Group 1: 66, 58, 64,48,58,65,52,57,54,58

Group 2: 66, 59, 64,58,62,59,57,66,54,58.

Can you suggest a statistical test to compare frequency of red blood cells in two groups?

How to compare two samples of frequencies ? – ResearchGate. Available from: https://www.researchgate.net/post/How_to_compare_two_samples_of_frequencies [accessed Aug 21, 2016].

**Contents**hide

#### Best Answer

If these are red blood cell counts for a fixed volume of blood, then the regression residuals for this type of data is often very well approximated by a normal distribution. Often a log transformation is very helpful when cell counts can be quite low with various suggestions available for 0 counts – e.g. using 0.5 cells or considering it a censored observation with a concentration of <1 cell/volume. Thus, things like ANOVA/ANCOVA/t-test etc. may be appropriate for this type of data (non-parametric methods like rank tests are of course also reasonable and the loss of efficiency is often relatively negligible – although group sizes are pretty small, so parametric approaches are likely worth it), if group allocation was by randomization – otherwise some additional adjustments (e.g. propensity scores) may be needed to account for the observational nature of the data, depending on what one tries to do.

### Similar Posts:

- Solved – How to compare frequencies among groups
- Solved – approach for comparing two groups of frequency distributions
- Solved – prop.test or chi squared test on count data with 3 groups
- Solved – Difference in frequencies in two groups of unequal size
- Solved – Can Fisher’s exact test accept a ‘vector of probabilities’