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!