I don't understand your reply... sorry. I'll try again. This may be a
self-evident solution for you, but I'll need a simple and concrete example.
Here is where I am right now:
If you have unequal n's, and want to determine linear parameters, you can
develop new coefficients by taking the normal unweighted coefficients
(e.g., -1, 0, +1, for three group design) and the formula:
n1(X1) + n2(X2) + n3(X3)/ n1+n2+n3 where the X's are 1, 2, and 3
because you have 3 groups. This gives you a new mean of the Xs... (i.e., no
longer 1+2+3/3 = 2), and from there you calculate the new coefficients
(e.g., 1 - ?, 2 - ?, 3 - ?, gives you the new linear coefficients) for the
3-group design with unequal n's. From there you can do things like determine
the the weighted linear estimated parameters. They are given in the spss
oneway printout... as I understand it... i.e., the weighted (for sample
size) beta for the linear contrast.
I calculated and checked this value with a data set in which the n's were
247, 29, and 37, for X1, X2, and X3 respectively. It worked. Now I want to
calculate the weighted quadratic beta for this data set. To do this I need
a formula.. for weighting... as above... but that formula above does not
work for the quadratic parameter because it is for a linear not a quadratic
trend. One text referred to a 1965 article by Gaito...for determining the
coefficients, but I don't have access to that paper at this moment. So I
asked, does anyone know this formula? If your answer IS the correct answer
to my question, perhaps you would kindly explain it to me in a more concrete
way suitable to my simple knowledge of the problem. My means are 2.05,
6.38, and 12.08 for the three groups respectively. In other words.. what
does one calculate and how?
Many thanks.
Duncan Murdoch <[EMAIL PROTECTED]> wrote in message
[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> On Tue, 30 Jan 2001 19:53:03 -0500, "K. Bloom" <[EMAIL PROTECTED]>
> wrote:
>
> >Could someone please tell me how to calculate quadratic coefficients for
> >unequal sample sizes (equal intervals, three groups)? The formula is not
in
> >the SPSS algorithm notes.
>
> Maybe I'm misunderstanding the question, but if you only have 3
> groups, your estimates will interpolate the group means. Just solve
> the 3 linear equations in 3 unknowns, using whatever equation solving
> method you like.
>
> Duncan Murdoch
>
>
>
>
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