Changes of a false negative I don't want to confuse anyone any further but I do think that it is important to reiterate one of Kurt's earlier points. All of the numbers being tossed around (% found positive with this or that test) are based upon 101 'CFS' people (however that was defined) in a single study. The chances of a false negative are entirely dependent upon the incidence in the population and the population of CFS patients is as poorly defined as W. Reeves could have ever hoped. This is an exaggeration of nearly any realistic scenario (but sometimes exaggerating the elements of an issue is useful in identifying pitfalls); say you have a lousy test that only correctly identifies one of every two patients with a particular disease but that disease only occurs in one of every 1000 people. You're going to get one positive test in 2000 tests. HALF of the positives will be missed but there will only one out of 2000 that got a false negative. Again, these numbers are extreme but they raise some of the central questions about testing accuracy. And this is only one half of the equation. There is the whole issue of false positives. So, when you ask if there is a one in three chance that a negative result is a false negative, that cannot be answered right now because there are way too few patients in the WPI study and I can't name a single variable that I don't expect to change at least to some degree over the next several months as more studies are completed (In Dr. Bateman's excellent speech she predicts that in some cohorts, the number of positive XMRV tests will be no higher than the positives in the controls). And on top of all this, we don't know what, if any, the true relationship is between XMRV and CFS. From where I sit, there is a huge amount to be excited about and there is a lot of reason for hope (and quite frankly, nearly all of the subjective, 'backstage' signs look good - people on the inside who are talking keeping staying excited, movement at the NIH, Ivy League Colleges opening positions dedicated to CFS and XMRV etc.). But as anxious as I am to "find out" for myself, I would not have a clue as to what to do with a negative (or positive) XMRV test at this point in time.