Posted by
Bridgette Portman on
Mar 08, 2011; 7:41am
URL: http://spssx-discussion.165.s1.nabble.com/Anova-SS1-vSS3-using-v-17-0-tp3412630p3413610.html
Hi everyone,
This is a rather elementary statistics question and I feel kind of stupid
asking it. But I've managed to thoroughly confuse myself. I hope someone
can help me out.
I've collected survey data from 260 respondents. As I'm analyzing
demographic information, I have noticed that the distribution of ages in
my sample is not normal. In fact, it is bimodal, with peaks around 20 and
60, and a trough around 40. This was due to my sampling method, not to any
intrinsic pattern in the population I was sampling from. I want to be able
to compare ages between various groups, such as men and women, in my
sample. But can I use a t-test, given the abnormal distribution? Should I
use a nonparametric test like Mann-Whitney U instead?
The reason I'm confused is that the bimodality is in my sample alone, do
to my sampling technique. The ages in the population as a whole, I'm sure,
has an underlying normal distribution. I am studying political activists,
and in order to get at them, I sampled from a) college student political
clubs, and b) actual political parties. The college kids tended to be
around 20, while the party people were 50+. I know one alternative would
be to just recode age into something like "below 40" and "above 40" but
I'd rather avoid doing that if I can.
Can anyone offer advice?
Thanks,
Bridgette
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