Slide 1OutlineFundamental Measures in EpidemiologySlide 4Example: Blood Pressure and StrokeRisk factorBlood Pressure as an Outcome: SPRINT in the news (9/11/15)Incidence & PrevalenceIncidenceSlide 10PrevalenceSlide 12Slide 13PrevalenceImportant considerations!Important considerations!Incidence and prevalence ratesSlide 18Importance of using ratesRelative RiskSlide 21Relative Risk InterpretationRelative Risk Interpretation Percent relative riskQuintiles of fitness (treadmill time) and mortality riskOther TermsOther TermsPopulation attributable riskCalculation of person–time yearssummaryConcepts and Methods 1: Outcomes, Risk factors, and other important termsFall 2017Outline•Risk Factors•Incidence•Prevalence•Other terminologyFundamental Measures in Epidemiology•Identify what we are measuring (disease, death, risk factor)= outcome•Factors related to the outcome i.e. physical activity, sedentary behavior = exposure•How do we express these measures in a way that –1) makes sense to people –2) can be compared across studies or populationsExample…Prevalence of children 6 to 19 years of age who attained sufficient moderate to vigorous physical activity to meet public health recommendations (≥60 minutes per day on 5 or more of the 7 days preceding the survey), by sex and age (National Health and Nutrition Examination Survey: 2003–2004). Go A S et al. Circulation. 2014;129:e28-e292Copyright © American Heart Association, Inc. All rights reserved.Example: Blood Pressure and Stroke•Identified from correlation between the presence of the factor and subsequent development of the disease.•Used as an outcome measure in a studyRisk factor1) Associated with the disease 2) Changing the risk factor changes the risk for diseaseBlood Pressure as an Outcome: SPRINT in the news (9/11/15)•population: 9300 Men and women over 50•2 groups:1) Standard of Care Group: Current BP reduction recommendations (<140mmHg)2) Lower BP reduction (<120mmHg)•120mmHg BP reduction group reduced CV events by 1/3 and death by ¼ compared with Standard group•Trial was stopped early!!Incidence & PrevalenceHow common is a disease, symptom or problem in a population?What are the chances that I will develop a disease?Incidence•Incidence: number of new occurrences of an outcome that develop during specified time period in population at risk•Cases where health status changes- Alive to dead, not injured to injured, not sick to sick = new occurrences during a given period of time Total population at risk•Example: what is the number of tollbooth workers on the NJ turnpike that developed lung cancer in the past 3 years?Prevalence•Prevalence: proportion of individuals that exhibit outcome of interest at a set time-point or length of time. Example: in 2010, there were 25.8 million americans with diabetes Prevalence =# people with outcome at a specified time# people in population at risk at specified timeAge-adjusted prevalence trends for high blood pressure in adults ≥20 years of age by race/ethnicity, sex, and survey (National Health and Nutrition Examination Survey: 1988–1994, 1999–2004, and 2005–2008).Circulation 2012;125:e2-e220Copyright © American Heart Association1988–2008 No Leisure-Time Physical Activity Trend ChartPrevalence•Function of incidence and duration•Prevalence can increase due to:–Increase in number of cases (incidence)–Length of time cases have disease before dying or recovering•Example: –Super-flu that kills within 5 hours. • prevalence will be low even if incidence is high –Regular-flu that lasts 3 months• prevalence will be higher, even if there were lower incidence ratesImportant considerations!•Low prevalence–Could mean rapid death or rapid cure–Not necessarily low incidence•Therefore, should not use prevalence data alone –Unsure of correct interpretationImportant considerations!•How to use prevalence rates–Survey of a city finds coronary heart disease is prevalence is particularly high–Therefore local hospital should consider opening cardiac rehabilitation center•High prevalence does not necessarily mean high risk for getting CHD•Could reflect increases survival because good emergency services and medical care that increase survival •People are living longer with the disease due to good managementIncidence and prevalence rates•Rate = number of cases/average population size•Incidence and prevalence rates can be expressed per some power of 10 (per 100 [percent], per 1000, per 10000) are usually less than 1 •9 deaths per 1000 individuals in the population per year–Death rate is 0.009 – or 0.9%Importance of using rates•Doctor reports 100 patellar tendon ruptures in runners in the past year–How big is the problem? - –Is running cause of problem? -•No information about number of people at riskRelative Risk•Relative risk is a ratio of the probability of the event occurring in the exposed group versus a non-exposed group. = probability in exposed/ probability in unexposed= a/(a+b) c/(c+d)RiskCardiovascular diseasePresent AbsentOverweight A (20) B (80)Normal weight C (2) D (100)•100 overweight•102 normal-weight1. Probability in exposed 20/(20+80) = .2 2. Probability in unexposed 2/(2+100) = .02 3. Determine ratio =10 4. Interpret: overweight are 10 times more likely to develop CVD than normal weightRiskCardiovascular diseasePresent AbsentOverweight A (20) B (80)Normal weight C (2) D (100)Relative Risk Interpretation•What does it mean if RR=1•- there is no difference in risk between the exposed and unexposed group•What does it mean if the RR in the “exposed group” is <1?•i.e RR for CVD in physically active people is .6 compared with inactive people (RR=1 )•What does it mean if the RR in the “exposed group” is >1?•i.e RR for CvRelative Risk InterpretationPercent relative risk•When RR in the “exposed group” is >1?–Percent increase = (RR-1)*100–I.e RR of 3.5 = (3.5-1)*100= 250% greater risk for CVD in smokers compared with non-smokers •When RR in the “exposed group” is <1?–Percent decrease = (1- RR)*100–i.e RR of .55= (1-.55)*100= 45% lower risk for prostate cancer in men who met PA guidelines compared with those who did notQuintiles of fitness (treadmill time) and mortality riskFitness groupMen WomenRelative risk1 (low) 3.44 4.652 1.37 2.423 1.46 1.434 1.17 0.765 (high) 1.00 1.00Lowest fitness groups had highest risk of deathBlair et al.,