liesdamned liesand statistics we have not considered that causes each in factas it happensthe flu virus survives considerably longer in cool dry air than it does in warm wet airand in north america both the flu season and school sessions are correlated with cooler and dryer weather given enough retrospective datait is always possible to find two variables that are correlatedas illustrated by the chart on the right when such correlations are foundthe first thing to do is to ask whether there is plausible theory explaining the correlation falling prey to the cum hoc ergo propter hoc fallacy can be quite dangerous at the start of roughly six million american women were being prescribed hormone replacement therapy (hrtin the belief that it would substantially lower their risk of cardiovascular disease that belief was supported by several highly reputable published studies that demonstrated reduced incidence of cardiovascular death among women using hrt many womenand their physicianswere taken by surprise when the journal of the american medical society published an article asserting that hrt in fact increased the risk of cardiovascular disease how could this have happenedre-analysis of some of the earlier studies showed that women undertaking hrt were likely to be from groups with better than average diet and exercise regimes perhaps the women undertaking hrt were on average more health conscious than the other women in the studyso that taking hrt and improved cardiac health were coincident effects of common cause statistical measures don' tell the whole story there are an enormous number of different statistics that can be extracted from data set by carefully choosing among theseit is possible to convey variety of different impressions about the same data good antidote is to look at the data set itself in the statistician anscombe published paper containing the table below it contains the coordinates of the points in each of four data sets stephen johnson"the trouble with qsar (or how learned to stop worrying and embrace fallacy), chem inf model nelson hdhumphrey llnygren pteutsch smallan jd postmenopausal hormone replacement therapyscientific review jama ; : -