[R] lm with data=(means,sds,ns)
kjetil@entelnet.bo
kjetil at entelnet.bo
Sun Apr 18 14:55:01 CEST 2004
On 18 Apr 2004 at 2:27, Ted Harding wrote:
> Hi Folks,
>
> I am dealing with data which have been presented as
>
> at each x_i, mean m_i of the y-values at x_i,
> sd s_i of the y-values at x_i
> number n_i of the y-values at x_i
>
> and I want to linearly regress y on x.
You need weighted regresseion, so lm with the argument weights.
Assuning constant variance of the errors, you can calculate
w[i] <- n_i
and put mean m_i of the y-values at x_i into y,
x_i values into x, n)- values into n. Then
lm(y ~ x, weight=n)
Kjetil Halvorsen
>
> There does not seem to be an option to 'lm' which can
> deal with such data directly, though the regression
> problem could be algebraically expressed in these terms.
>
> One way of fudging it would be to replace each m_i by
> a set of n_i numbers Y_i constructed as
>
> u_i <- rnorm(ni)
>
> Y_i <- m_i + s_i*(u_i - mean(u_i))/sd(u_i)
>
> and associate these with X_i <- rep(x_i,n_i), thereby
> constructing a regression-equivalent set of pseudo "raw data"
> which could be fed to lm(Y~X). However, this strikes me as
> cumbersome, at least, and even ugly!
>
> Is there a direct way to go from {(n_i,m_i,s_i)} to the
> fitted regression, with summaries and all (and use of 'predict')?
>
> With thanks,
> Ted.
>
>
> --------------------------------------------------------------------
> E-Mail: (Ted Harding) <Ted.Harding at nessie.mcc.ac.uk> Fax-to-email: +44
> (0)870 167 1972 Date: 18-Apr-04
> Time: 02:27:50 ------------------------------ XFMail
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