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HPCSA Board Exam Epidemiology and Biostatistics — practice by topic

Browse 34 questions across 1 Epidemiology and Biostatistics topics. Choose what you want to revise, then open a question to check its answer and worked solution.

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Epidemiology and Biostatistics topics

Measures of Risk (34)

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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 →

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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