Chronic fatigue syndrome (CFS) is a debilitating disease of unknown etiology that is estimated to affect 17 million people worldwide. In a case-control observational study, researchers identified DNA from a human gamma-retrovirus (XMRV) in 68 of 101 patients with CFS (67%) compared with 8 of 218 healthy controls (3.7%). We want to know if these data show evidence of a relationship between XMRV and CFS. Under the null hypothesis of no relationship between XMRV and CFS, what is the expected count of patients with CFS and XMRV?

Question

Quizplus · Accepted Answer

To calculate the expected count under the null hypothesis of no relationship between XMRV and CFS, we use the formula for expected counts in a contingency table. The total number of individuals is 101 (patients with CFS) + 218 (healthy controls) = 319. The total number of individuals with XMRV is 68 (patients with CFS and XMRV) + 8 (healthy controls with XMRV) = 76. The expected count of patients with CFS and XMRV is calculated as (Total CFS patients * Total XMRV positive) / Total individuals = (101 * 76) / 319 = 24.1.

Chronic Fatigue Syndrome (CFS) Is a Debilitating Disease of Unknown