This tool allows an exploration of departures from HWE at a single disease locus given 
a genetic disease model.  

For examining a sample of affected cases:  

The "data type" should be set to "case".  Choose a genetic model from the list (dominant, 
recessive, additive, multiplicative). Set a GRR (gamma). Enter the allele frequency at 
the bi-allelic locus for the entire population, as well as a threshold (p-value). Hit 
"Compute sample size".  A window will pop up on the screen: Delta_p is the disequilibrium 
coefficient for departures from HWE in cases, Qp is the expected allele frequency for cases, 
Lambda_s is the expected sibling relative risk ratio, and the sample size is the number of 
cases needed to expect to see departures from HWE at the specified threshold.  

For examining a sample of unaffected controls:  

The "data type" should be set to "control".  Choose a genetic model from the list (dominant, 
recessive, additive, multiplicative). Set a Kp (population prevelance) or alpha  (baseline 
risk for wild-type homozygotes), as well as a GRR (gamma).  Enter the allele frequency at the
bi-allelic locus for the entire population, as well as a threshold (p-value).  Hit "Compute 
sample size". A window will pop up on the screen:  Delta_c is the disequilibrium coefficient 
for departures from HWE in controls, Qc is the expected allele frequency for controls, Lambda_s 
is the expected sibling relative risk ratio, and the sample size is the number of controls needed 
to expect to see departures from HWE at the specified threshold.  

All calculations for determining the sample sizes needed to expect to observed departures from 
HWE use a central chi-square test (corresponding to 50% power).