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USMLE Step 1 Measures of Risk — practice questions

Explore 34 free Measures of Risk questions in USMLE Step 1 Epidemiology and Biostatistics. Open each question or exercise to read its content, reference answers and available explanation.

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Measures of Risk questions and exercises with answers

Showing questions 1–30 of 34.

What distinguishes a ratio from a proportion?Read the answer and worked solution →Among men in a follow-up study, 3,151 were nondiabetic and 189 were diabetic. What is the ratio of nondiabetic to diabetic men?Read the answer and worked solution →Delaware's infant mortality rate in 2001 was 10.7 per 1,000 live births and New Hampshire's was 3.8 per 1,000. What is the ratio of the two rates?Read the answer and worked solution →In 2002 the United States reported 15,075 new tuberculosis cases and 802 tuberculosis deaths. What is the death-to-case ratio per 100 new cases?Read the answer and worked solution →A follow-up study recorded 1,494 deaths in all, of which 911 occurred among men. What proportion of the deaths were among men?Read the answer and worked solution →Which fraction qualifies as a proportion?Read the answer and worked solution →How is morbidity defined?Read the answer and worked solution →At a corporate picnic, 99 people ate potato salad and 30 of them developed gastroenteritis. What is the food-specific attack rate?Read the answer and worked solution →Eighteen primary shigellosis cases arose in 18 households holding 86 people in all, and 17 contacts later fell ill. What is the secondary attack rate?Read the answer and worked solution →A cohort produced 16 new cases of heart disease over 6,400 person-years of observation. What is the incidence rate per 1,000 person-years?Read the answer and worked solution →Under the half-year convention, how much disease-free follow-up does a participant diagnosed during year 3 contribute?Read the answer and worked solution →Observation of a cohort participant stops at one of four end points. Which event is not one of them?Read the answer and worked solution →In 2003 there were 44,232 new AIDS cases in a mid-year population of 290,809,777. What is the incidence rate per 100,000?Read the answer and worked solution →Of 1,150 women surveyed in Maine, 468 reported frequent multivitamin use before pregnancy. What is the prevalence of frequent use?Read the answer and worked solution →The United States recorded 2,419,921 deaths in 2003 in a population of 290,809,777. What is the crude mortality rate per 100,000?Read the answer and worked solution →Which mortality rate divides by the estimated total mid-year population?Read the answer and worked solution →The neonatal mortality rate counts deaths among children of which age?Read the answer and worked solution →Which denominator and multiplier does the maternal mortality rate use?Read the answer and worked solution →A hepatitis A epidemic produced 555 cases and 3 of the case-patients died. What is the case-fatality rate?Read the answer and worked solution →Which two end points are most commonly used for years of potential life lost?Read the answer and worked solution →Leukemia killed 125 children in the age group whose midpoint is 2.5 years. Using an end point of 65 years, what is the years of potential life lost for that group?Read the answer and worked solution →Leukemia accounted for 117,033 years of potential life lost among 252,755,000 people under age 65. What is the YPLL rate per 1,000?Read the answer and worked solution →In a prison outbreak, 28 of 157 East wing inmates and 4 of 137 West wing inmates developed tuberculosis. What is the risk ratio for East against West?Read the answer and worked solution →In the prison outbreak 28 East wing inmates fell ill and 129 stayed well, while 4 West wing inmates fell ill and 133 stayed well. What is the odds ratio?Read the answer and worked solution →In a case-control study, 32 of 40 case-patients and 20 of 80 controls had stored maize indoors. What is the odds ratio for indoor storage?Read the answer and worked solution →Infirmary visits for acute respiratory illness ran at 11.6 per 1,000 tourists per week in 1998 against 5.3 in 1997. What is the rate ratio?Read the answer and worked solution →Lung cancer mortality was 0.57 per 1,000 per year among light smokers and 0.07 among nonsmokers. What is the attributable proportion?Read the answer and worked solution →At a wedding, 50 of 53 cake eaters and 4 of 26 non-eaters fell ill. What share of illness among cake eaters is attributable to the cake?Read the answer and worked solution →Varicella struck 11.8% of vaccinated children and 42.9% of unvaccinated children. What is the vaccine effectiveness?Read the answer and worked solution →Work out the measureRead the answer and worked solution →

Worked practice questions

What distinguishes a ratio from a proportion?

  1. A ratio's numerator need not sit inside its denominator
  2. A ratio must always be reported as a percentage figure
  3. A ratio can compare only two rates, never two counts
  4. A ratio always needs a multiplier of 100 or larger
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Correct answer: A. A ratio's numerator need not sit inside its denominator

1. A ratio is the relative magnitude of two quantities, and the two quantities need not be related at all. 2. A proportion is a special kind of ratio in which the numerator is a subset of the denominator, so a part is compared with its whole. 3. Apples divided by oranges is therefore a ratio but not a proportion, while apples divided by all fruit is both. 4. Percentages, multipliers and the choice between rates and counts are presentation decisions, so none of them separates the two measures. _Source: CDC Principles of Epidemiology in Public Health Practice (3rd ed., US federal, public domain), Lesson 3 "Measures of Risk", section Definition of proportion_

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Among men in a follow-up study, 3,151 were nondiabetic and 189 were diabetic. What is the ratio of nondiabetic to diabetic men?

  1. 0.06 to 1
  2. 16.7 to 1
  3. 5.7 to 1
  4. 17.7 to 1
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Correct answer: B. 16.7 to 1

1. A ratio divides the count in one group by the count in the other, so the nondiabetic count goes on top: 3,151 divided by 189. 2. 3,151 divided by 189 equals 16.67, which rounds to 16.7. 3. Ratios are usually rescaled so the denominator becomes 1, giving 16.7 to 1. 4. Turning the fraction over, 189 divided by 3,151, gives 0.06 to 1, the same comparison read backwards. 5. Putting the total of 3,340 men on top gives 17.7 to 1, and 189 out of 3,340 as a percentage gives 5.7, neither of which is the ratio asked for. _Source: CDC Principles of Epidemiology in Public Health Practice (3rd ed., US federal, public domain), Lesson 3 "Measures of Risk", section Method for calculating a ratio_

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Delaware's infant mortality rate in 2001 was 10.7 per 1,000 live births and New Hampshire's was 3.8 per 1,000. What is the ratio of the two rates?

  1. 6.9 to 1
  2. 0.4 to 1
  3. 2.8 to 1
  4. 14.5 to 1
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Correct answer: C. 2.8 to 1

1. Rates can form the numerator and denominator of a ratio just as counts can. 2. Divide the Delaware rate by the New Hampshire rate: 10.7 divided by 3.8 equals 2.816. 3. Rounded to one decimal place that is 2.8, reported as 2.8 to 1. 4. Subtracting instead of dividing gives 6.9, which is a difference in rate, not a ratio. 5. Adding gives 14.5 and inverting gives 0.4, so both of those describe something other than Delaware relative to New Hampshire. _Source: CDC Principles of Epidemiology in Public Health Practice (3rd ed., US federal, public domain), Lesson 3 "Measures of Risk", section Method for calculating a ratio_

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