[visionlist] How to compute d' when hit rate or false alarm rate is 0 or 1?

[Todd S. Horowitz]

Dear Hang,

The common approach is to substitute 1/2N errors for 0 (where N is 
the number of trials).

Todd

At 10:03 PM +0800 6/3/07, Hang Zhang wrote:
>Hi,
>
>In signal detection theory, sensitivity d' is computed as the 
>z-score difference between false alarm rate and hit rate. I am 
>puzzled about what is the z-score for a 0 or 1 rate, because 
>theorically the value is indefinite. But an indefinite d' for an 
>observer in a psychological experiment seems unreasonable... Could 
>someone tell me how to compute d' when hit rate or false alarm rate 
>is 0 or 1? Many Thanks.
>
>Best,
>Hang
>
>----------------------------------------------------
>Hang ZHANG, PhD Candidate
>State Key Laboratory of Brain and Cognitive Science
>Institute of Psychology, Chinese Academy of Sciences
>4A, Datun Road, Chaoyang District
>Beijing 100101, China
>Tel: 8610 6483 7209
>Fax: 8610 6487 2070
>Email: zhangh at psych.ac.cn
>----------------------------------------------------
>
>
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-- 
Todd S. Horowitz, Ph.D.
Instructor in Ophthalmology
Harvard Medical School

Visual Attention Laboratory
Brigham & Women's Hospital
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