Course Notes - Department of Mathematics and Statistics

• Therefore r 2 = 0.8931, so 89.31% of the variation in the bloodpressure is explained by the stress levels.Some important notes• Correlation does not imply causation• Sometimes we accidentally intepret the causation in reverse.• It was found that the more firemen fighting a fire, the bigger thefire is going to be. Therefore conclude firemen cause fires.• In reality the more severe the fire, the more firemen who are sent.• Another common mistake is ignoring a third factor• As ice cream sales increase, the rate of drowning deaths increasessharply. Therefore, ice cream causes drowning.• In this situation we are ignoring the fact that ice cream sales anddrowning both increase in summer, so summer is actually thecause of both these increases.• Another example of ignoring a 3 rd factor.• A study found that sleeping with one’s shoes on is strongly correlatedwith waking up with a headache. Therefore it was concludedsleeping with one’s shoes on causes headache.• In this example the researcher has ignored the more plausibleexplanation that both events are caused by a 3 rd factor, in thiscase going to bed drunk.• And then there is just straight coincidence.• With a decrease in the number of pirates, there has been an increasein global warming over the same period. Therefore, globalwarming is caused by a lack of pirates.229