Example of a significant net difference test
This example tests whether the difference between working and non-working women who have tried non-alcoholic wine in London is significantly different from the difference between the same groups of women in Manchester. The column labeled ABCD shows the value of the T statistic for each row.
The Quantum program is:
tab wine women;op=2;nopc;c=c132'2';decp=0
tstat ntd;elms=ABCD
l women
n11TOTAL
n00;c=c231'1'
n23London;hdlev=1;unl1
n01Works;c=c149'12';id=A
n01Does!Not!Work;c=c149n'12';id=B
n00;c=c231'2'
n23Manchester;hdlev=1;unl1
n01Works;c=c149'12';id=C
n01Does!Not!Work;c=c149n'12';id=D
n23;hdlev=1
stat ntd,ABCD
l wine
n10TOTAL
n00;c=c111'1/7'
col 111;Past 7 days;1-2 weeks;2-4 weeks;1-3 months;3-6 months;
+over 6 months
n00
n01Never tried non-alcoholic wine;c=-
The table it produces is:
London Manchester
------------- --------------
Does Does
Not Not
TOTAL Works Work Works Work ABCD
(A) (B) (C) (D)
TOTAL 1800 572 440 382 384
Past 7 days 23 35 20 23 11
1-2 weeks 15 19 15 12 11
2-4 weeks 13 15 10 17 11
1-3 months 12 8 15 23 6 25
3-6 months 6 8 5 6 6
Over 6 months 6 4 5 6 11
Never tried non- 24 12 30 14 43 -11
alcoholic wine
-----------------------------------------------
NTD: Columns Tested (5% risk level) - A/B/C/D |
This example shows that there are significant differences in the 1-3 months and Never tried rows. However you cannot tell the degree of significance from these results. For that you need to look at the P-values.
See also