Course Notes - Department of Mathematics and Statistics

Mobile phone example• Human exposure to radiofrequency has increased dramaticallyduring recent years from widespread use of mobile phones. Handheldmobile phones were introduced in Sweden during the late1980’s. This case control-control study was carried out to testthe hypothesis that long-term mobile phone use increases the riskof brain cancer.Brain TumourMobile Phone Use Yes No TotalNever/rarely 155 275 430Regularly 118 399 517273 674 947Odds RatioOR = 118/399155/275OR = 0.52• Those who use mobile phones have 0.52 times the odds of a braintumour compared with those who do not.• There is actually a PROTECTIVE effect from using mobilephones - The odds are 48% less for mobile phone users comparedwith those who do not use mobile phones.• Is it significant though? Need to calculate the confidence interval.Confidence interval for Odds Ratio - Mobile phone exampleln(OR) ± 1.96 × s.e.(ln(OR))• Our OR was 0.52, so using our calculator we get ln(0.52) = -0.654• The s.e.(ln(OR)) is√1s.e.(ln(OR)) =155 + 1275 + 1118 + 1399s.e.(ln(OR)) = 0.1449150