NR-503 WEEK 8 FINAL EXAM 2026/2027 | Population Health
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SECTION 1: EPIDEMIOLOGIC PRINCIPLES & STUDY DESIGNS (Questions 1-15)
Question 1
A public health nurse wants to determine the current prevalence of undiagnosed type 2
diabetes in a community. She randomly selects 2,000 adults, measures fasting blood
glucose, and calculates the proportion with elevated values. Which study design is
being used?
A. Cohort study
B. Case-control study
C. Cross-sectional study
D. Ecologic study
Correct Answer: C. Cross-sectional study
Rationale: A cross-sectional study measures both exposure and outcome
simultaneously at a single point in time (or over a brief period), providing a "snapshot" of
disease prevalence in a population. This design is ideal for estimating prevalence and
,generating hypotheses but cannot establish temporality or incidence. Students often
confuse cross-sectional studies with cohort studies; the key distinction is that
cross-sectional studies lack a time dimension for following participants forward. Cohort
studies follow exposed and unexposed groups over time to measure incidence.
Question 2
A researcher identifies 150 patients newly diagnosed with ovarian cancer and 300
matched controls without cancer. She interviews all participants about their lifetime
talcum powder use. What type of study design is this?
A. Prospective cohort study
B. Retrospective cohort study
C. Case-control study
D. Randomized controlled trial
Correct Answer: C. Case-control study
Rationale: This is a classic case-control study: participants are selected based on
disease status (cases with ovarian cancer, controls without), and past exposure (talcum
powder use) is assessed retrospectively. Case-control studies are efficient for rare
diseases and diseases with long latency periods but are susceptible to recall bias. The
directionality is backward (from outcome to exposure), distinguishing them from cohort
studies, which are forward-directional (from exposure to outcome). Matching controls
to cases on age and other factors reduces confounding.
,Question 3
A researcher enrolls 5,000 nurses who smoke and 5,000 nurses who do not smoke. She
follows both groups for 20 years, recording lung cancer incidence. What type of study
design is this, and what measure of association can be directly calculated?
A. Case-control study; odds ratio
B. Cross-sectional study; prevalence ratio
C. Cohort study; risk ratio (relative risk)
D. Ecologic study; correlation coefficient
Correct Answer: C. Cohort study; risk ratio (relative risk)
Rationale: This is a prospective cohort study: participants are classified by exposure
status (smoking) at baseline and followed forward in time to measure disease
incidence (lung cancer). Cohort studies allow direct calculation of incidence rates and
risk ratios (relative risk, RR = incidence in exposed / incidence in unexposed). The RR is
the preferred measure of association for cohort studies because it directly compares
disease risk between exposed and unexposed groups. Students frequently confuse RR
with OR; RR can only be calculated in cohort studies, not case-control studies.
Question 4
, A researcher notes that countries with higher per capita olive oil consumption have
lower rates of cardiovascular disease mortality. She uses country-level aggregate data
to examine this relationship. What is the primary limitation of this study design?
A. Inability to control for confounding variables
B. The ecological fallacy—assuming group-level associations apply to individuals
C. Small sample size due to limited number of countries
D. Inability to calculate measures of association
Correct Answer: B. The ecological fallacy—assuming group-level associations apply to
individuals
Rationale: This is an ecologic study, which uses group-level (aggregate) data rather than
individual-level data. The ecological fallacy occurs when inferences about individuals
are made based on group-level associations. For example, countries with high olive oil
consumption may have lower CVD mortality, but this does not prove that individuals
who consume more olive oil have lower CVD risk—other factors (Mediterranean diet
pattern, physical activity, healthcare access) may explain the association. Ecologic
studies are useful for generating hypotheses but cannot establish causality at the
individual level.
Question 5
A pharmaceutical company conducts a double-blind, placebo-controlled trial of a new
antihypertensive medication in 10,000 patients with stage 2 hypertension. Participants
Epidemiology & Biostatistics Reviewer | Download to Score
an A | Pass Guaranteed - A+ Graded
SECTION 1: EPIDEMIOLOGIC PRINCIPLES & STUDY DESIGNS (Questions 1-15)
Question 1
A public health nurse wants to determine the current prevalence of undiagnosed type 2
diabetes in a community. She randomly selects 2,000 adults, measures fasting blood
glucose, and calculates the proportion with elevated values. Which study design is
being used?
A. Cohort study
B. Case-control study
C. Cross-sectional study
D. Ecologic study
Correct Answer: C. Cross-sectional study
Rationale: A cross-sectional study measures both exposure and outcome
simultaneously at a single point in time (or over a brief period), providing a "snapshot" of
disease prevalence in a population. This design is ideal for estimating prevalence and
,generating hypotheses but cannot establish temporality or incidence. Students often
confuse cross-sectional studies with cohort studies; the key distinction is that
cross-sectional studies lack a time dimension for following participants forward. Cohort
studies follow exposed and unexposed groups over time to measure incidence.
Question 2
A researcher identifies 150 patients newly diagnosed with ovarian cancer and 300
matched controls without cancer. She interviews all participants about their lifetime
talcum powder use. What type of study design is this?
A. Prospective cohort study
B. Retrospective cohort study
C. Case-control study
D. Randomized controlled trial
Correct Answer: C. Case-control study
Rationale: This is a classic case-control study: participants are selected based on
disease status (cases with ovarian cancer, controls without), and past exposure (talcum
powder use) is assessed retrospectively. Case-control studies are efficient for rare
diseases and diseases with long latency periods but are susceptible to recall bias. The
directionality is backward (from outcome to exposure), distinguishing them from cohort
studies, which are forward-directional (from exposure to outcome). Matching controls
to cases on age and other factors reduces confounding.
,Question 3
A researcher enrolls 5,000 nurses who smoke and 5,000 nurses who do not smoke. She
follows both groups for 20 years, recording lung cancer incidence. What type of study
design is this, and what measure of association can be directly calculated?
A. Case-control study; odds ratio
B. Cross-sectional study; prevalence ratio
C. Cohort study; risk ratio (relative risk)
D. Ecologic study; correlation coefficient
Correct Answer: C. Cohort study; risk ratio (relative risk)
Rationale: This is a prospective cohort study: participants are classified by exposure
status (smoking) at baseline and followed forward in time to measure disease
incidence (lung cancer). Cohort studies allow direct calculation of incidence rates and
risk ratios (relative risk, RR = incidence in exposed / incidence in unexposed). The RR is
the preferred measure of association for cohort studies because it directly compares
disease risk between exposed and unexposed groups. Students frequently confuse RR
with OR; RR can only be calculated in cohort studies, not case-control studies.
Question 4
, A researcher notes that countries with higher per capita olive oil consumption have
lower rates of cardiovascular disease mortality. She uses country-level aggregate data
to examine this relationship. What is the primary limitation of this study design?
A. Inability to control for confounding variables
B. The ecological fallacy—assuming group-level associations apply to individuals
C. Small sample size due to limited number of countries
D. Inability to calculate measures of association
Correct Answer: B. The ecological fallacy—assuming group-level associations apply to
individuals
Rationale: This is an ecologic study, which uses group-level (aggregate) data rather than
individual-level data. The ecological fallacy occurs when inferences about individuals
are made based on group-level associations. For example, countries with high olive oil
consumption may have lower CVD mortality, but this does not prove that individuals
who consume more olive oil have lower CVD risk—other factors (Mediterranean diet
pattern, physical activity, healthcare access) may explain the association. Ecologic
studies are useful for generating hypotheses but cannot establish causality at the
individual level.
Question 5
A pharmaceutical company conducts a double-blind, placebo-controlled trial of a new
antihypertensive medication in 10,000 patients with stage 2 hypertension. Participants
