Example of a T-test on column proportions
This example tests the differences between the proportions of people trying various types of wine in London and Manchester. In the comparison between columns B and D (women in London and women in Manchester) a significant difference has been found for those trying brand A: the letter D beside the figure for women in column B indicates that the proportion of women in London is significantly larger than the proportion of women in Manchester. A similarly significant difference exists between columns C and D for brand A. The other comparisons in that row (columns A and B, and A and C) do not produce significant differences at the 90% level.
The program written for this test was:
tab wine ban01;op=2;nopc
tstat prop;elms=AB,CD,AC,BD;clevel=90
l ban01
n00;c=c231'1'
n23London;hdlev=1;unl1
col 132;Male;%id=A;Female;%id=B
n00;c=c231'2'
n23Manchester;hdlev=1;unl1
col 132;Male;%id=C;Female;%id=D
l wine
n10Base
col 111;Brand A;Brand B;Brand C;Brand D;Brand E;Brand F;
+Brand G
n01Non;c=-7
The table produced is:
London Manchester
-------------------- -----------------------
Male Female Male Female
(A) (B) (C) (D)
Base 90 86 90 73
Brand A 8 9D 9D 2
Brand B 8 11 14A 11
Brand C 18B 9 11 10
Brand D 8 6 7 10
Brand E 21 23 24 22
Brand F 6 9 7 6
Brand G 21 19D 20D 12
None 10 14 10 27CB
-------------------------------------------------------------
Proportions: Columns Tested (10% risk) AB / CD / AC / BD |
In this example, the test was carried out using a 90% confidence level. This means that significant differences at this level are shown in the table. To see the actual level of significance, you need to look at the P-values.
See also