I constructed a contingency table with three categorical variables (species, elevation, and year) and performed a chi-square analysis to test for independence between them. My initial goal was to determine the probability that observed differences in species elevational ranges between two surveys (years) were due to chance.
The test revealed a significant relationship between the variables. This, however, presents me with a new question: how do I go about determining precisely where this relationship exists (e.g. species & elevation vs. species & year vs.elevation & year, etc.)?
Any advice or suggestions on how I can figure this out? Thanks!
Hi Evan,
Your best bet would be to undertake multiple Chi Sqs, and the easiest way to do this is in SPSS Amos. If you dont have this, you can probaly get a free trial and, if not, a good academic rate.
Good luck
You can recategorize/subgroup.
Otherwise, SPSS and R have nominal by nominal comparisons available.
Hope this helps
Matt
Tony Alderton Paul Yarnold Matthew Kerry thanks very much for the helpful advice!
Paul Yarnold regarding your suggestion that elevation be defined as ordered (opposed to categorical); would the same also be true of elevational zones? I should have been clearer in making that distinction.
For the sake of clarity, here is a breakdown of the variables/attributes:
- Year= 2 (baseline survey; resurvey)
- Species= 3 (count: species A; species B; species C)
- Elevation= 3 (low; mid; high)
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