Signal detection theory

[Robert Ariel]

Tobias,

Computationally, C is the average of the your transformed hit and false
alarm rates.  You can see this in the equation you presented.  So, no doubt
if you have equal false alarms rates across conditions, differences in C are
resulting because of differences in hit rates.

Basically with equal false alarm rates, the condition with a higher hit rate
will always be more liberal.  If hit rates are equal, the condition with
higher false alarm rate will be more liberal.

Best,

Robert

On Fri, Apr 16, 2010 at 9:59 AM, Tobias <tobias.fw at gmail.com> wrote:

> Hi together,
>
> this might be a bit off topic but as you are all very much into
> psychological experimental science you might be of great help for this
> issue. Besides, my topic is the outcome of an E-Prime experiment ;)
>
> It is about the response bias in signal detection theory (SDT). I've
> heard that C is usually better than Beta as a measure of response bias
> as it is indpendent of d'. Now what I have in my experiment is a very
> high hit rate for condition A and a lower hit rate for condition B.
> False alarm rates are however the same for A and B. So what I get
> using the formula for C (C = -0.5*(z(false alarms) + z(hits)) is a
> liberal criterion C for A and a less liberal criterion for B.
>
> So can I actually say that A is more liberal? Apparently this is only
> due to the fact that the hit rate is higher. I am quite puzzled by
> this... glad for any help!
>
> Tobias
>
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