Posted by
Art Kendall on
Dec 04, 2010; 1:19pm
URL: http://spssx-discussion.165.s1.nabble.com/test-on-means-for-subgroups-vs-total-tp3278152p3292124.html
YMMV but in my experience, when people say they want to "test one
group against the total" they mean several things.
<soapbox> It is important to tease out the precise question.
<\soapbox>
Sometimes they mean they want something like a standard score type
idea, i.e., how extreme is
this subpop in the whole pop of
which it is a part. [mean vs grand mean] This can be problematical
when a large portion of the cases are on both sides of the
comparison. [IQ this class vs norms.]
Sometimes they mean that they want to compare
this subpop to
all of the other members of the pop without regard to which subpop
they in (1 residual subpop). [mean a vs mean of all residual cases
(cases not a)] This can compare apples to all other fruit.
Sometimes they mean that they want to compare
this subpop to
each of the other subpops. [mean a vs mean b, mean a vs mean
c, etc, but not b vs c etc.]
Sometimes they mean that they want to compare
each pair of
subpops.[All pairs of means]
Sometimes when the subpops are ordered they want to compare ordered
subpops to the lowest value for any subpop. (e.g., doses vs zero
dose).
aside: Does anyone know of a site that succinctly lays out in one
place 1) statements like those above 2) specifies the names for
kinds of contrasts 3) gives examples and 4) gives some
visualizations?
Art Kendall
Social Research Consultants
On 12/3/2010 10:21 PM, R B wrote:
I didn't respond to this post initially because the question pertained
to excel. But, since someone responded, I would like to point out that
it is possible to compare the mean of one group against the grand
mean. I recently showed how to do this in SPSS via the MIXED procedure
employing the TEST subcommand. Really, there are several procedures in
SPSS that could be used to carry out this type of contrast.
Ryan
On Fri, Dec 3, 2010 at 4:26 PM, Richard Ristow [hidden email] wrote:
At 04:45 AM 11/24/2010, Alexandra Chirilov wrote:
Could you help me with an excel which perform test on means for
subgroups vs. total?
None of the standard tests compare subgroups with the total; they
compare non-overlapping subgroups with each other.
The general term for comparing subgroup means is 'analysis of
variance' ('ANOVA'). There are many variations on ANOVA, but the
place to start is with a simple one-way ANOVA, unless there's reason
in your study to do otherwise. (A still better place to start is to
get advice from someone who knows the statistical methods and the
details of your study, who can tell what methods would be appropriate.)
If you want to do this in Excel, the main advice you'll get here is,
don't. Lots of people do statistical analysis in Excel, but the
general professional opinion is that Excel isn't very good for that,
and there are many risks in using it.
If you have SPSS, and can load your data into SPSS, from the menus try
Analyze > Compare Means > One-Way ANOVA
You *must* have someone statistically knowledgeable help you to
understand the results. You can also post SPSS and statistical
questions here, though there's no substitute for someone you can talk
with face to face.
-Best of luck,
Richard Ristow
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Art Kendall
Social Research Consultants