Re: ANOVA QUESTION - Terminology

jp wrote:
I have looked at an intro to biostatistics book.

I know two groups is t-test and more than two is ANOVA. I'm sorry this

ANOVA can also be done with two groups. The F-ratio from the ANOVA equals the square of the t-ratio for the same data.

sounds so basic, but I didn't find any example of this in the book.
Most examples of ANOVA are 3 groups of race (Chinese, White, Black)
with one dependent variable (IQ). I can see how this is a one-way as
there is one independent and one dependent. When repeated measures is
described in the book, the ANOVA now changes to something like
monitoring heart rate at several times during biking. A two-way is
described as having two independent variables, say gender and race in
which IQ is again, the dependent variable.

The question I have is what would the analysis be for for what I was
suggesting above. To me you could treat it as a two-way in that Group
(A,B,C) and Test# (Pre Post) could serve as two independent variables,
but to me I thought it sounded like a repeated measures because the
Test Score was the dependent variable measured at two time points.
There is no example like this in my book, and perhaps I not understand
it. I would imagine this newsgroup is for individuals of all learning
levels?

To me, this sounds like a two-way design, but I am confused because it
is more like a one-way repeated measures since the dependent variable
is measured twice and there is the independent variable Group. I would
really like to know if this distinction.

It is a two-way design. Nowadays, some people do call it a repeated measures design, probably because the procedure they use in their stats package is found under "GLM->Repeated Measures", or something similar. In textbooks, however, it would more likely be described as a split-plot design, a between-within design, or a mixed design. Group is a between-subjects factor, and Time (pre vs post) is a within-subjects (or repeated measures) factor. (How you label it no doubt varies by area of research.)

The design has 3 F-tests: Main effect of Group, main effect of Time, and the Group x Time interaction. The null hypothesis for the interaction is that change is equivalent in all of the groups. The interaction F-test is equivalent to an independent groups t-test on the change scores.

But, as Rich Ulrich noted, another very common method of analysis for data such as this is one-way ANCOVA. It is a linear regression model of this form:

Post = b0 + b1*Pre + b2*Group

Here is a comment you might find useful.

www.angelfire.com/wv/bwhomedir/notes/krantz_ancova.txt

--
Bruce Weaver
bweaver@xxxxxxxxxxxx
www.angelfire.com/wv/bwhomedir
.

Relevant Pages

  • Re: ANOVA QUESTION - Terminology
    ... I know two groups is t-test and more than two is ANOVA. ... Most examples of ANOVA are 3 groups of race ... and Test# could serve as two independent variables, ... a repeated-measures analysis with several ...
    (sci.stat.consult)
  • Re: ANOVA QUESTION - Terminology
    ... I know two groups is t-test and more than two is ANOVA. ... It is a two-way design. ... and there are second order interactions to ...
    (sci.stat.consult)
  • Re: ANOVA QUESTION - Terminology
    ... I know two groups is t-test and more than two is ANOVA. ... I thought it was abundantly clear from the context of jp's immediately preceding statement that I was talking about the F-ratio from a one-way ANOVA and the t-ratio from an independent groups t-test. ... To me, this sounds like a two-way design, but I am confused because it ...
    (sci.stat.consult)
  • Re: ANOVA QUESTION - Terminology
    ... I know two groups is t-test and more than two is ANOVA. ... But that is usually done in LINEAR MODELS after the introduction ... and Test# could serve as two independent variables, ... a repeated-measures analysis with several ...
    (sci.stat.consult)
  • Re: Multiple single-sample t-tests
    ... We can carry out a two-way ANOVA, with A and B as repeated factors. ... we also want to compare the values of X to a given value: ... take into account the dependancy due to the repeated measure design. ... multiple single-sample t-tests. ...
    (sci.stat.consult)