CPH CERTIFIED IN PUBLIC HEALTH — PRACTICE EXAM | 200
Multiple Choice Questions with Rationales**
*Based on the NBPHE CPH Exam Content Outline (Effective
August 1, 2024)*
DOMAIN 1: DATA, ANALYTICS, AND INFORMATICS (12%)**
**Question 1**
In a case-control study examining the association between smoking and lung cancer, the
investigators selected 500 individuals with lung cancer and 500 without lung cancer, then
assessed their smoking history. What measure of association can be directly calculated from this
study design?
A) Relative risk
B) Attributable risk
C) Odds ratio (correct answer)
D) Prevalence ratio
**Rationale:** A case-control study begins by identifying cases (those with the disease) and
controls (those without), then looks backward to assess exposure history. Because the
investigator determines the number of cases and controls, incidence cannot be calculated
directly. The odds ratio is the measure of association used in case-control studies, as it
compares the odds of exposure among cases to the odds of exposure among controls.
---
**Question 2**
,A public health department reports that the age-adjusted mortality rate from heart disease in
County A is 185 per 100,000, while the crude rate is 220 per 100,000. What does this difference
most likely indicate?
A) County A has excellent hospitals
B) County A has a younger population than the standard population (correct answer)
C) Heart disease is underreported
D) The standard population is younger
**Rationale:** Age adjustment allows comparison of mortality rates between populations with
different age structures. If the crude rate (220) is higher than the age-adjusted rate (185), it
suggests County A has an older population than the standard population used for adjustment.
Conversely, if the crude rate were lower than the adjusted rate, it would suggest a younger
population.
---
**Question 3**
In a normal distribution, approximately 95% of observations fall within:
A) One standard deviation of the mean
B) Two standard deviations of the mean (correct answer)
C) Three standard deviations of the mean
D) Four standard deviations of the mean
**Rationale:** The empirical rule (68-95-99.7 rule) states that in a normal distribution,
approximately 68% of observations fall within 1 standard deviation, 95% within 2 standard
deviations, and 99.7% within 3 standard deviations of the mean. This is fundamental for
calculating confidence intervals and interpreting statistical significance.
,---
**Question 4**
A screening test for diabetes has a sensitivity of 90% and a specificity of 85%. If the test is
applied to a population with a disease prevalence of 10%, what happens to the positive
predictive value (PPV) if the same test is applied to a population with a prevalence of 2%?
A) PPV increases
B) PPV decreases (correct answer)
C) PPV remains the same
D) PPV becomes 100%
**Rationale:** Positive predictive value is the proportion of positive test results that are true
positives. As disease prevalence decreases in the tested population, the number of false
positives relative to true positives increases, thereby decreasing PPV. This is known as the false
positive paradox and explains why screening low-prevalence populations yields many false
positives even with good tests.
---
**Question 5**
A public health researcher wants to study the relationship between air pollution exposure and
asthma exacerbations across multiple cities while controlling for temperature and humidity.
Which statistical approach is most appropriate?
A) Simple linear regression
B) Multiple regression (correct answer)
C) Chi-square test of independence
, D) Paired t-test
**Rationale:** Multiple regression allows examination of the relationship between one
dependent variable (asthma exacerbations) and multiple independent variables (air pollution
exposure, temperature, humidity) simultaneously, while controlling for the effects of the other
variables. Simple linear regression only accommodates one independent variable.
---
**Question 6**
In systematic sampling, the researcher selects:
A) Every element from the population
B) Every kth element from a list of the population after a random start (correct answer)
C) Elements most convenient to access
D) Elements based on specific characteristics
**Rationale:** Systematic sampling involves selecting every kth element from a sampling frame
after a random starting point is chosen, where k equals the population size divided by the
desired sample size. It is simpler than simple random sampling but assumes no periodic pattern
in the sampling frame that could introduce bias.
---
**Question 7**
A confidence interval of 95% for a relative risk of 1.5 ranges from 1.1 to 2.0. What does this
indicate?
Multiple Choice Questions with Rationales**
*Based on the NBPHE CPH Exam Content Outline (Effective
August 1, 2024)*
DOMAIN 1: DATA, ANALYTICS, AND INFORMATICS (12%)**
**Question 1**
In a case-control study examining the association between smoking and lung cancer, the
investigators selected 500 individuals with lung cancer and 500 without lung cancer, then
assessed their smoking history. What measure of association can be directly calculated from this
study design?
A) Relative risk
B) Attributable risk
C) Odds ratio (correct answer)
D) Prevalence ratio
**Rationale:** A case-control study begins by identifying cases (those with the disease) and
controls (those without), then looks backward to assess exposure history. Because the
investigator determines the number of cases and controls, incidence cannot be calculated
directly. The odds ratio is the measure of association used in case-control studies, as it
compares the odds of exposure among cases to the odds of exposure among controls.
---
**Question 2**
,A public health department reports that the age-adjusted mortality rate from heart disease in
County A is 185 per 100,000, while the crude rate is 220 per 100,000. What does this difference
most likely indicate?
A) County A has excellent hospitals
B) County A has a younger population than the standard population (correct answer)
C) Heart disease is underreported
D) The standard population is younger
**Rationale:** Age adjustment allows comparison of mortality rates between populations with
different age structures. If the crude rate (220) is higher than the age-adjusted rate (185), it
suggests County A has an older population than the standard population used for adjustment.
Conversely, if the crude rate were lower than the adjusted rate, it would suggest a younger
population.
---
**Question 3**
In a normal distribution, approximately 95% of observations fall within:
A) One standard deviation of the mean
B) Two standard deviations of the mean (correct answer)
C) Three standard deviations of the mean
D) Four standard deviations of the mean
**Rationale:** The empirical rule (68-95-99.7 rule) states that in a normal distribution,
approximately 68% of observations fall within 1 standard deviation, 95% within 2 standard
deviations, and 99.7% within 3 standard deviations of the mean. This is fundamental for
calculating confidence intervals and interpreting statistical significance.
,---
**Question 4**
A screening test for diabetes has a sensitivity of 90% and a specificity of 85%. If the test is
applied to a population with a disease prevalence of 10%, what happens to the positive
predictive value (PPV) if the same test is applied to a population with a prevalence of 2%?
A) PPV increases
B) PPV decreases (correct answer)
C) PPV remains the same
D) PPV becomes 100%
**Rationale:** Positive predictive value is the proportion of positive test results that are true
positives. As disease prevalence decreases in the tested population, the number of false
positives relative to true positives increases, thereby decreasing PPV. This is known as the false
positive paradox and explains why screening low-prevalence populations yields many false
positives even with good tests.
---
**Question 5**
A public health researcher wants to study the relationship between air pollution exposure and
asthma exacerbations across multiple cities while controlling for temperature and humidity.
Which statistical approach is most appropriate?
A) Simple linear regression
B) Multiple regression (correct answer)
C) Chi-square test of independence
, D) Paired t-test
**Rationale:** Multiple regression allows examination of the relationship between one
dependent variable (asthma exacerbations) and multiple independent variables (air pollution
exposure, temperature, humidity) simultaneously, while controlling for the effects of the other
variables. Simple linear regression only accommodates one independent variable.
---
**Question 6**
In systematic sampling, the researcher selects:
A) Every element from the population
B) Every kth element from a list of the population after a random start (correct answer)
C) Elements most convenient to access
D) Elements based on specific characteristics
**Rationale:** Systematic sampling involves selecting every kth element from a sampling frame
after a random starting point is chosen, where k equals the population size divided by the
desired sample size. It is simpler than simple random sampling but assumes no periodic pattern
in the sampling frame that could introduce bias.
---
**Question 7**
A confidence interval of 95% for a relative risk of 1.5 ranges from 1.1 to 2.0. What does this
indicate?
