analyte specificity and sample size

Hello,

The table below shows the incidence of Crohn's Disease and Celiac
Sprue serological markers in disease state samples.


For Celiac sprue the markers and their incidence are as follows:
AGA IgA (80-90%),
tTG IgA (97%),
AGA IgG (75-85%),
tTG IgG (56.6%),


For Crohn's Disease:
ASCA IgA (36.5%),
ASCA IgG (45.5%),


How many diagnosed samples are required in order to calculate the
disease state sensitivity and specificity for each of the 6 analytes
(above) toward their respective diseases?


The table above has the percent incidence of the serological markers
for the two disease states, Celiac Sprue and Crohn's Disease. I assume

the gating factor will be the analyte of the lowest incidence for each
of the diseases. So, this wouold be tTG IgG for Celiac and ASCA IgA
for Crohn's. Am I correct?


I would like to learn how to calculate the required number of disease
state positive samples, and negatives for two levels of uncertainty in
the concordance values: ± 5% and ± 10%. I


The prevalence among the general population of Crohn's Disease in North

America is 0.026 to 0.198%, while that of Celiac Disease is 0.5 to 1%.
How many normal samples are required?


I am grateful for any help you can offer. Dr. Martin Holt, of
Medstats, has graciously referred me to the article: Determination of
Sample Size by Nyi Nyi Naing, which provides a good starting point.
(Please see his response on Medstats, July 8th to my initial posting of
this
question.)


Thanks!


Andie

.

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