I'm trying to separate two groups of values from a single data set. I can assume that one of the populations is normally distributed and is at least half the size of the sample. The values of the second one are both lower or higher than the values from the first one (distribution is unknown). What I'm trying to do is to find the upper and lower limits that would enclose the normally-distributed population from the other.
My assumption provide me with starting point:
- all points within the interquartile range of the sample are from the normally-distributed population.
I'm trying to test for outliers taking them from the rest of the sample until they don't fit into the 3 st.dev of the normally-distributed population. Which is not ideal, but seem to produce reasonable enough result.
Is my assumption statistically sound? What would be a better way to go about this?
p.s. please fix the tags someone.