Fisher-Freeman-Halton Exact Test or Jonckheere–Terpstra test - which is the most appropriate?

Posted by DP_Sydney on Feb 15, 2016; 6:50am
URL: http://spssx-discussion.165.s1.nabble.com/Fisher-Freeman-Halton-Exact-Test-or-Jonckheere-Terpstra-test-which-is-the-most-appropriate-tp5731524.html

Hi,

Analysis question: I am seeking to determine whether there is a relationship between the extent of pigment in tail feathers of a particular bird species and the extent of pigment on 1) the foreneck (5 x 5 table, n = 40) and 2) the wings (4 x 5 table, n = 80). Pigment was scored on an ordinal scale from least to most pigment for each body region (5 levels for tail and foreneck, 4 levels for wing). Because of the small sample size. A chi-square contingency table is inappropriate because of the high proportion of expected values <5.

Option 1 - Fisher-Freeman-Halton Exact Test: Both contingency tables have a high number of zero cells: 12 in the 5 x 5 table, 6 in the 4 x 5 table. Is this a problem for this test?

Option 2 - Jonckheere–Terpstra test: At first glance, this test is appropriate since both my variables are ordinal variables and I expect a positive relationship (i.e. birds with more pigment on the tail are predicted to have more pigment on the foreneck or wing). However, I am not postulating a causal relationship between variables (i.e. pigment on tail vs pigment on foreneck/wing). Is this test appropriate for analyses where the independent and dependent variables are interchangeable? 

Any advice as to which option is the most suitable, and any other issues that I have not identified, is most welcome!

Thanks,
Dean