Assignment on Wickham study (pdf)
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Added on 2019-11-12
Assignment on Wickham study (pdf)
Added on 2019-11-12
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NameGomez, AndrewHomework 2:Measures of occurrence and morality, Kaplan Meier (Epi I, fall 2017)Please show your work! Please email to dshoham@luc.edu and ebenson3@luc.edu by Monday 9/11 by 11am CT.The risk is a proportion, not a rate. Proportions do not have any units (or at least, the units cancel out, as in “4 out of 5 dentists prefer Trident gum”. Rates always have time in the denominator, as in “55 miles per hour.” Risk is the number of people who develop disease, divided by the number of people “at risk” of that disease over a period of time. More exactly, cumulative incidence is a measure of risk. Youcan think of it as a percentage (proportion per 100 people), but sometimes it is too rare for percentage to be useful; in this case it might be the number of cases per 100,000 or per million. People are “at risk” if they can develop the disease. For example, men are not at risk for ovarian cancer, because they lack ovaries (however, men are at risk for breast cancer, becausemen do have breasts; it just isn’t as common). Usually, our goal is just to calculate the risk, but to compare risk in two groups: those exposed to some risk factor, and those not exposed.In this 2x2 table, we put the disease status or mortality along the top (columns), and the exposure status or risk factor along the side (rows). In this simple case, we’ll use a classic example: smoking and lung cancer. As in the Wickham study (from Rothman’s Epidemiology: An Introduction), there were 20 years of follow-up between smoking assessment and the end of the study; subjects could develop lung cancer at any point over the followup period.Developedlung cancerDidn’t developlung cancerTotal number “at risk” of lung cancerPerson smoked7504,2505,000Person did not smoke2509,75010,000Total1,00014,00015,000Answer the following 4 questions related to this hypothetical study.1.What is the proportion of smokers in the population (at the beginning of the study)? That is, what percentage smokes?SolutionProportionofSmokers=No.ofSmokersTotalPopulation=500015000∗100%=33.33%2.What proportion of the total population develops lung cancer (over the 20 years of follow-up)?Solution
Proportionofpopdevelopedcancer=No.ofpeopledevelopedcancerTotalPopulation=100015000∗100%=6.67%3.What is the 20-year risk of lung cancer among smokers?SolutionCancerRiskamongSmoker=No.ofpeopledevelopedcanceramongsmokersTotalPopulationofsmokers∗20=7505000∗20=34.What is the 20-year risk of lung cancer among non-smokers?SolutionCancerRiskamongnon−smoker=No.ofpeopledevelopedcanceramongnon−smokersTotalPopulationofnon−smokers∗20=25010000∗20=0.5Table A below shows the number of new breast cancer cases over the 5-year period and the average populations at risk for each age and race group.Table A.5.Calculate the age specific 5-year breast cancer incidence rates per 100,000 for white and black women in the table above.SolutionAgespecificincidencerate=NewcancercasesduringtheyearEstimatedpopulation∈thesameyearofthepop∗100000First case of 0-19 for the White females is;Agespecificincidencerate=914373000∗100000=0.06162For the whole age groups the age-specific incidence rates are given below;White FemalesBlack femalesAge No. Population % of 5-year incidence rate No. Population % of 5-year incidence rate
groupof casesin 1000'spopulation per 100000of casesin 1000'spopulation per 1000000-19914373330.0602122410.0020-293197210174.4254955185.6530-39204952681238.903186391249.7740-496773478611141.5264052710121.4450-5910247483111212.117914529175.0060-69947735438267.496403056209.8470-79736022995320.143921483264.8680+434811993362.64156621251.61Total100100Question 6: Life Table and Kaplan MeierPersonNo.12345678910Jan2004Mar2004May2004Jul2004Sep2004Nov2004Jan2005Mar2005May2005Jul2005Sep2005Nov2005Jan2006Calendar TimeD (1)D (17)D (20)D (9)C (16)C (2)C (10)(24)D (13)D (3)The above graphic is a hypothetical cohort of 10 persons followed for up to 24 months after treatment between January 2004 and January 2006. D, death; C, censored observations; ( ), duration of follow-up in months (all assumed to be exact whole numbers). Note that person #5, 7, and 9 were administratively censored as they made it to the end of the follow-up period.6A. Reorganize the data so that the time scale is transformed to follow-up time rather calendar time. (1 point)
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