I'm doing some research to establish the ED50 of a cocktail of
medication. The sequential up-down method for small samples appeals to
me, because it substantially reduces the number of participants in the
trial.
However, in similar trials in which analysis is done by the
up-and-down method the number of participants is estimated by
conservative power analysis. The advantage of the small sample size is
then gone.
Is anyone familiar with the up-and-down procedure as described by
Dixon and Massey (Introduction to Statistical Analysis, 4th ed,
McGraw-Hill)? I have the following questions:
1. Can you tell me when the procedure for small samples is
appropriate.
2. What are the advantages of the procedures with large N's, compared
to the small sample variant.
3. In Dixon's text book I did not find how to determine the confidence
interval for small samples. Lichtman (1998) determines the 95%
confidence interval in the test for small samples as:
1.96 x dose increment x (SQR 2/n).
in which n= the last n trials and 1.96 reflects the 0.05 alpha level.
Is this equation correct? It would mean that the CI depends primarily
on the dose increment.
4. Finally what is meant by the term "last n trials".
Thank you for your help!
Rothi
[EMAIL PROTECTED]
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