[R] bimodal data

(Ted Harding) Ted.Harding at nessie.mcc.ac.uk
Fri Dec 2 14:36:04 CET 2005

On 02-Dec-05 Simone Immler wrote:
>     Hi,
>   Does anybody have a good tip of how to treat bimodal data to
> perform statistical analyses? My data set ranges from -1 to 1
> (any values are posssible in between) and most data are either
> close to -1 or close to 1. They are the results of a two choice
> experiment where individuals could choose more than once in
> either direction and scores were calculated.
>   Simone

Frankly, I suspect you will do better to analyse at the level of
the original choices, rather than the final "scores", for two

1. It will probably be easier, more straightforward, and more
tractable to set up a statistical model for the binary choices;

Distributions which (as I infer from your description) are highly
"U-shaped" are tricky to model, and do not lend themselves to
the conventional types of analysis at all well.

2. Because "scores were calculated" you have probably lost
useful information.

One issue that may be informative (which you do not specify) is
whether the number of choices made varies from subject to subject
and, if so, how many choices did each subject make.

Hoping this helps, and please come back with more detail if it
might help to make progress.

Best wishes,

E-Mail: (Ted Harding) <Ted.Harding at nessie.mcc.ac.uk>
Fax-to-email: +44 (0)870 094 0861
Date: 02-Dec-05                                       Time: 13:35:55
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