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Usual settings for the transformed up-down procedure
Dear list members (and transformed up-down user in particular),
we are extending our MLP software
(http://www.psy.unipd.it/~grassi/mlp.html) to the transformed up-down
adaptive procedure so the user of our software can decide to run a given
threshold-experiment with either the maximum likelihood procedure or the
transformed up-down (wow! what a fun!).
We are now working on the software and facing the first problem: what
are the "traditional" settings for the transformed up-down?
- how many "downs"?
- how many reversals before stopping the procedure?
- how many reversal with a small step-size and how many with a large one?
- how many step-sizes?
- what's the (is there any) "usual" ratio between small and large step-size?
- how to calculate the subject's threshold?
Here the traditional rules base on my own reading:
- Number of "downs". I found only studies using the 2(or 3)-down 1-up.
No study using the 4-down (or higher) 1-up rule. Furthermore, no study
using the 1-down, 2/3/4...-up.
- Reversals and step-size. So far I found that people tend to use two
step sizes only (e.g., factor 2 and factor 2^(1/2), i.e., sqrt(2)) and
to run 4 reversals with the large step size and 8 (or 12) reversals with
the small step size.
- For the threshold calculation I found that it is usually calculated on
the last 8 (or 12) reversals points of a given block. Moreover, I found
that people calculate indifferently arithmetic, geometric mean or median.
I'm particularly interested in exceptions to the "traditional rules" I
found: we want to include these exceptions to our software.
Thank you in advance for the help you can provide,