Statistic in Health Care Management Week 2 Critical Reflection Paper: Chapters 3 & 4 Objective: To critically reflect your understanding of the readings and your ability to apply them to your Health c
Chapter 3 Quantifying the Extent of Disease Critical Components of RCT • Randomization • Control Group – Ethical Issues • Monitoring – Interim Analysis – Data and Safety Monitoring Board • Data Management • Reporting Learning Objectives • Define and differentiate prevalence and incidence • Select, compute and interpret the appropriate measure to compare the extent of disease between groups • Compare and contrast, c ompute and interpret relative risks, risk differences, and odds ratios Prevalence • Proportion of participants with disease at a particular point in timebaseline at examined persons of Number disease with persons of Number Prevalence Point Example 3.1. Computing Prevalence Free of CVD History of CVD Total Men 1548 244 1792 Women 1872 135 2007 Total 3420 379 3799 Prevalence of CVD = 379/3799 = 0.0998 = 9.98% Prevalence of CVD in Men = 244/1792 = 0.1362 = 13.62% Prevalence of CVD in Women = 135/2007 = 0.0673 = 6.73% Example - H1N1 Outbreak • H1N1 outbreak first noticed in Mexico • Large outbreak early on in La Gloria -a small village outside of Mexico City. • Studied extensively in the first report on H1N1 (Fraser, Donelly et al. “Pandemic potential of a strain of Influenza (H1N1): early findings”, Science Express , 11 May 2009.) • Important questions: Who is most likely to be impacted? What are the characteristics of people commonly impacted? Computing Prevalence Age No ILI ILI Total < 44 years 703 522 1225 > 44 years 256 94 350 Total 959 616 1575 Data on H1N1 outbreak in La Gloria, Mexico.
n=1575 villagers (out of 2155) were surveyed to determine if they had influenza like illness (ILI) between 2/15/09 and 4/27/09. Computing Prevalence Age No ILI ILI Total < 44 years 703 522 1225 > 44 years 256 94 350 Total 959 616 1575 Prevalence of ILI=616/1575=0.3911=39.11% Prevalence of ILI in < 44=522/1225=0.4261=42.61% Prevalence of ILI in >44=94/350=0.2686=26.86% Incidence • Likelihood of developing disease among persons free of disease who are at risk of developing diseasebaseline at risk at persons of Number period specified a during disease develop who persons of Number Incidence Cumulative free disease are persons which during time of lengths the of Sum period specified a during disease develop who persons of Number Rate Incidence Computing Incidence • Cumulative incidence requires complete follow - up on all participants • Person - time data is used to take full advantage of available information in incidence rate • Incidence rate often expressed as an integer per multiple of participants over a specified time Incidence of CVD? 1 Disease - Free 2 CVD 3 Death 4 Disease - Free 5 CVD 0 5 10 Yrs Study Start Incidence Ratefree disease are persons which during time of lengths the of Sum period specified a during disease develop who persons of Number Rate Incidence Incidence of CVD Incidence = 2/(10+9+3+10+5) = 2/37 = 0.054 5.4 per 100 person - years Example 3.2. Computing Incidence Develop CVD Total Follow - Up Time (years) Men 190 9984 Women 119 12153 Total 309 22137 Incidence Rate of CVD in Men = 190/9984 = 0.01903 = 190 per 10,000 person -years Incidence Rate of CVD in Women = 119/12153 = 0.00979 = 98 per 10,000 person -years Computing Incidence Developed ILI Total Follow -Up Time (years) < 44 years 522 20,064 > 44 years 94 3,514 Total 616 23,578 Incidence Rate of ILI in < 44 = 522/20064 = 0.0260 = 260 per 10,000 person -years Incidence Rate of ILI in >44 = 94/3514 = 0.0268 = 268 per 10,000 person -years Comparing Extent of Disease Between Groups • Risk difference (excess risk)unexposed exposed unexposed exposed unexposed exposed Rate Incidence Rate Incidence Incidence Cumulative Incidence Cumulative Prevalence Prevalence Comparing Extent of Disease Between Groups • Risk difference of prevalent CVD in smokers versus non -smokers Free of CVD History of CVD Total Non -Smoker 2757 298 3055 Current Smoker 663 81 744 3420 379 3799 = 81/744 – 298/3055 = 0.1089 – 0.0975 = 0.0114smokers- non smokers Prevalence Prevalence Population Attributable Risk of CVD in Smokers vs Non - Smokers Free of CVD History of CVD Total Non -Smoker 2757 298 3055 Current Smoker 663 81 744 3420 379 3799 = (0.0998 – 0.0975) / 0.0998 = 0.023 = 2.3%overall smokers- non overall Prevalence Prevalence Prevalence Comparing Extent of Disease Between Groups • Risk difference of history of ILI in Males and Females in La Gloria No ILI ILI Total Males 517 260 777 Females 442 356 798 959 616 1575 = 356/798 - 260/777 = 0.4461 – 0.3346 = 0.1115Males Females Prevalence Prevalence Comparing Extent of Disease Between Groups • Relative riskunexposed exposed Prevalence Prevalence Comparing Extent of Disease Between Groups • Relative risk of CVD in smokers versus non -smokers Free of CVD History of CVD Total Non -Smoker 2757 298 3055 Current Smoker 663 81 744 3420 379 3799 = 0.1089/0.0975 = 1.12smokers- non smokers Prevalence Prevalence Comparing Extent of Disease Between Groups • Relative risk of ILI in females versus males No ILI ILI Total Males 517 260 777 Females 442 356 798 959 616 1575 = 0.4461/0.3346 = 1.33males females Prevalence Prevalence Comparing Extent of Disease Between Groups • Odds ratio) Prevalence (1 Prevalence ) Prevalence (1 Prevalence unexposed unexposed exposed exposed Comparing Extent of Disease Between Groups • Odds ratio of CVD in hypertensives versus non - hypertensives No CVD CVD Total Non -hypertensive 2754 188 2942 Hypertensive 659 181 840 3413 369 378204.4 932.0/ 068.0 725.0/ 275.0 ) 2942/ 881 (1 188/2942 ) 840/ 181 (1 181/840 Comparing Extent of Disease Between Groups • Odds ratio of ILI in younger group versus older group Age No ILI ILI Total < 44 years 703 522 1225 > 44 years 256 94 350 Total 959 616 157502.2 731.0/ 269.0 574.0/ 426.0 ) 350/ 94 (1 94/350 ) 1225/ 522 (1 522/1225 Relative Risks and Odds Ratios • Not possible to estimate relative risk in case - control studies • Can estimate odds ratio because of its invariance property Invariance Property of Odds Ratio Cancer (Case) No Cancer (control) Total Smoker 40 29 69 Non -smoker 10 21 31 50 50 100 Case - control study to assess association between smoking and cancer Invariance Property of Odds Ratio Cancer (Case) No Cancer (control) Total Smoker 40 29 69 Non -smoker 10 21 31 50 50 100 Odds ratio for cancer in smokers versus non -smokers = (40/29) / (10/21) = 2.90 Odds of smoking in patients with cancer versus not = (40/10) / (29/21) = 2.90!