All questions
Question 1
A cross-sectional study surveys 2,000 high school students (ages 14–18) during a single semester to test whether energy drink use is associated with anxiety symptoms. Students complete anonymous questionnaires on weekly energy drink servings, sleep duration, and a validated anxiety scale; school nurses measure resting heart rate once. Results: 29% report at least 3 energy drinks/week; elevated anxiety scores are present in 34% overall, 45% among high users vs 30% among low/nonusers. High users also report shorter sleep and more social media use. Investigators state they cannot determine directionality.
Which bias is most likely to affect the results of this study?
- Temporal bias from unclear exposure-outcome sequence (correct answer)
- Recall bias because cases remember exposures better
- Cross-contamination due to treatment switching over time
- Selection bias because random sampling eliminates it
- Observer bias because anxiety scale is laboratory-based
Explanation: This question tests understanding of study design and evidence types in biostatistics and epidemiology. Study design involves choosing the appropriate methodology to answer a research question while minimizing bias. In this vignette, the described study design is a cross-sectional study, which is appropriate for associating energy drink use with anxiety at one time point. The correct answer identifies temporal bias from unclear exposure-outcome sequence as the main issue. A common misconception, as seen in choice B, is misidentifying the study design due to assuming recall bias dominates in concurrent assessments. Teaching strategies include emphasizing study design features and common biases, using real-world examples to illustrate abstract concepts, and practicing vignettes to identify design characteristics.
Question 2
Investigators conduct a case-control study to evaluate whether prior antibiotic exposure is associated with Clostridioides difficile infection (CDI). Cases are 220 hospitalized adults (median age 67) with positive toxin assay and diarrhea. Controls are 220 hospitalized adults on the same wards without diarrhea, matched by age and length of stay. Antibiotic exposure in the prior 90 days is abstracted from the electronic medication record. Results: 154/220 (70%) cases vs 110/220 (50%) controls received fluoroquinolones. The team notes that some controls later develop diarrhea after discharge, which is not captured.
What is the most appropriate next step in this study design?
- Improve control definition to avoid outcome misclassification (correct answer)
- Randomize patients to antibiotics to confirm causality
- Measure incidence of CDI prospectively in all patients
- Replace records with participant recall of antibiotics
- Exclude matched controls to increase generalizability
Explanation: This question tests understanding of study design and evidence types in biostatistics and epidemiology. Study design involves choosing the appropriate methodology to answer a research question while minimizing bias. In this vignette, the described study design is a case-control study, which is appropriate for associating antibiotic exposure with CDI. The correct answer identifies improving control definition to avoid outcome misclassification as the next step. A common misconception, as seen in choice B, is misidentifying the study design due to suggesting randomization in an observational context. Teaching strategies include emphasizing study design features and common biases, using real-world examples to illustrate abstract concepts, and practicing vignettes to identify design characteristics.
Question 3
A randomized controlled trial enrolls 300 adults aged 30–65 with newly diagnosed hypertension. Hypothesis: home blood pressure telemonitoring plus pharmacist titration improves BP control at 6 months versus usual care. Randomization is 1:1; participants cannot be blinded due to the device, but outcome measurement uses automated office BP by staff unaware of assignment. Results: controlled BP (<130/80) occurs in 62% intervention vs 48% usual care. The intervention group has more frequent contact with clinicians and reports improved medication adherence.
Which of the following best describes the study design used in this scenario?
- Randomized controlled trial comparing two management strategies (correct answer)
- Case-control study comparing controlled versus uncontrolled BP
- Cross-sectional study measuring BP at one visit
- Prospective cohort study observing telemonitoring uptake
- Ecologic study comparing clinics by device availability
Explanation: This question tests understanding of study design and evidence types in biostatistics and epidemiology. Study design involves choosing the appropriate methodology to answer a research question while minimizing bias. In this vignette, the described study design is a randomized controlled trial, which is appropriate for comparing telemonitoring to usual care for hypertension control. The correct answer identifies this as comparing two management strategies through randomization. A common misconception, as seen in choice D, is misidentifying the study design due to confusing it with observational cohorts. Teaching strategies include emphasizing study design features and common biases, using real-world examples to illustrate abstract concepts, and practicing vignettes to identify design characteristics.
Question 4
A prospective cohort study in 5,600 adults aged 45–75 without colorectal cancer tests whether processed meat intake increases cancer incidence over 10 years. Baseline diet is assessed by food frequency questionnaire; exposure categories are low, moderate, and high processed meat intake. Incident colorectal cancer is confirmed by pathology reports. Results: cancer occurs in 1.8% high intake vs 1.2% low intake. High intake participants also have lower fiber intake, higher alcohol use, and less screening colonoscopy at baseline. Investigators collect colonoscopy history but some records are missing.
Which bias is most likely to affect the results of this study?
- Confounding by screening behavior and lifestyle factors (correct answer)
- Recall bias because cancer diagnosis changes past diet
- Observer bias because pathology reports are unblinded
- Temporal bias because meat intake follows cancer onset
- Cross-contamination from controls receiving chemotherapy exposure
Explanation: This question tests understanding of study design and evidence types in biostatistics and epidemiology. Study design involves choosing the appropriate methodology to answer a research question while minimizing bias. In this vignette, the described study design is a prospective cohort study, which is appropriate for linking processed meat intake to colorectal cancer incidence. The correct answer identifies confounding by screening behavior and lifestyle factors as the bias. A common misconception, as seen in choice B, is misidentifying the study design due to assuming recall bias in baseline assessments. Teaching strategies include emphasizing study design features and common biases, using real-world examples to illustrate abstract concepts, and practicing vignettes to identify design characteristics.
Question 5
A cross-sectional study measures vitamin D levels and reports musculoskeletal pain in 700 outpatient adults aged 18–80 during winter months. Hypothesis: low vitamin D is associated with current chronic pain. Vitamin D is measured from a single blood draw; pain is assessed with a standardized questionnaire. Results: 42% have vitamin D deficiency; chronic pain is reported by 36% overall, 44% among deficient vs 30% among nondeficient. Many participants with pain report reduced outdoor activity and higher BMI. Investigators caution about confounding and directionality.
Which bias is most likely to affect the results of this study?
- Temporal bias because exposure-outcome timing is unclear (correct answer)
- Recall bias because cases overreport vitamin D labs
- Cross-contamination from randomized vitamin D supplementation
- Observer bias because vitamin D assays are subjective
- Selection bias because cross-sectional studies randomize subjects
Explanation: This question tests understanding of study design and evidence types in biostatistics and epidemiology. Study design involves choosing the appropriate methodology to answer a research question while minimizing bias. In this vignette, the described study design is a cross-sectional study, which is appropriate for associating vitamin D levels with musculoskeletal pain concurrently. The correct answer identifies temporal bias because exposure-outcome timing is unclear as the bias. A common misconception, as seen in choice B, is misidentifying the study design due to assuming recall bias in lab-based measurements. Teaching strategies include emphasizing study design features and common biases, using real-world examples to illustrate abstract concepts, and practicing vignettes to identify design characteristics.
Question 6
A multicenter randomized controlled trial enrolls 640 adults aged 45–79 with type 2 diabetes (mean A1c 8.4%, 52% women) and no prior myocardial infarction. Investigators test the hypothesis that adding once-daily “gliflozin-X” to metformin reduces major adverse cardiovascular events (MACE) over 3 years versus placebo. Participants are randomized 1:1 using a computer-generated sequence stratified by site; identical capsules are dispensed, and patients, clinicians, and outcome adjudicators remain blinded. Follow-up visits occur every 3 months; 8% are lost to follow-up, similar between groups. Results: MACE occurs in 44/320 (13.8%) in gliflozin-X vs 62/320 (19.4%) in placebo; hospitalization for heart failure occurs in 18/320 (5.6%) vs 31/320 (9.7%). Adverse events include genital infections in 27/320 (8.4%) vs 9/320 (2.8%). The investigators conclude the drug lowers MACE risk with acceptable safety in this population.
Which of the following best describes the study design used in this scenario?
- Prospective cohort study with exposure-based follow-up
- Randomized, double-blind, placebo-controlled clinical trial (correct answer)
- Cross-sectional prevalence survey at one time point
- Case-control study using retrospective exposure recall
- Ecologic study comparing group-level diabetes outcomes
Explanation: This question tests understanding of study design and evidence types in biostatistics and epidemiology. Study design involves choosing the appropriate methodology to answer a research question while minimizing bias. In this vignette, the described study design is a randomized, double-blind, placebo-controlled clinical trial, which is appropriate for testing the efficacy and safety of a new drug intervention in patients with type 2 diabetes. The correct answer identifies this as the precise study design, emphasizing randomization, blinding, and placebo use to reduce bias. A common misconception, as seen in choice A, is misidentifying the study design due to confusing it with observational cohort studies that lack intervention assignment. Teaching strategies include emphasizing study design features and common biases, using real-world examples to illustrate abstract concepts, and practicing vignettes to identify design characteristics.
Question 7
A university hospital follows a prospective cohort of 2,400 adults aged 50–75 without dementia at baseline (60% women; 30% with hypertension). Investigators test the hypothesis that chronic benzodiazepine use increases incidence of Alzheimer disease over 8 years. Exposure is defined from pharmacy refill records (≥90 days supplied per year). Annual cognitive screening and neurologist adjudication determine incident Alzheimer disease. Results: Alzheimer disease develops in 96/800 (12.0%) exposed vs 144/1,600 (9.0%) unexposed. Exposed participants have higher baseline anxiety and poorer sleep, and they attend follow-up visits less often. Investigators adjust for age, education, depression, and comorbidities, but they acknowledge persistent differences between groups.
Which bias is most likely to affect the results of this study?
- Selection bias from differential loss to follow-up (correct answer)
- Cross-contamination because controls receive benzodiazepines
- Recall bias because exposure is self-reported
- Observer bias because outcomes are laboratory values
- Temporal bias because dementia precedes exposure definition
Explanation: This question tests understanding of study design and evidence types in biostatistics and epidemiology. Study design involves choosing the appropriate methodology to answer a research question while minimizing bias. In this vignette, the described study design is a prospective cohort study, which is appropriate for measuring incident Alzheimer disease in relation to benzodiazepine exposure over time. The correct answer identifies selection bias from differential loss to follow-up, as exposed participants attend less often. A common misconception, as seen in choice C, is misidentifying the study design due to assuming recall bias in a prospective setup with records. Teaching strategies include emphasizing study design features and common biases, using real-world examples to illustrate abstract concepts, and practicing vignettes to identify design characteristics.
Question 8
A randomized controlled trial enrolls 210 adults (ages 19–55) with moderate persistent asthma and frequent nighttime symptoms despite inhaled corticosteroids. Investigators test the hypothesis that adding a new leukotriene antagonist reduces exacerbations over 24 weeks. Participants are randomized 1:1 using sealed, opaque envelopes prepared by an independent pharmacist; tablets are identical, and both patients and clinicians are blinded. Exacerbations are defined as need for systemic steroids or urgent visit. Results: 22/105 (21%) in treatment vs 35/105 (33%) in placebo have an exacerbation. However, 18% of participants correctly guess their assignment due to mild headache occurring more often in the active group (26% vs 10%).
What is the primary advantage of the study design described?
- It estimates disease prevalence in the population
- It reduces confounding through random assignment (correct answer)
- It is fastest for studying rare outcomes
- It avoids loss to follow-up by design
- It proves causation without any potential bias
Explanation: This question tests understanding of study design and evidence types in biostatistics and epidemiology. Study design involves choosing the appropriate methodology to answer a research question while minimizing bias. In this vignette, the described study design is a randomized controlled trial, which is appropriate for evaluating the efficacy of a new leukotriene antagonist in reducing asthma exacerbations. The correct answer identifies the study design's advantage, such as reducing confounding through random assignment. A common misconception, as seen in choice C, is misidentifying the study design due to overestimating its efficiency for rare outcomes. Teaching strategies include emphasizing study design features and common biases, using real-world examples to illustrate abstract concepts, and practicing vignettes to identify design characteristics.
Question 9
A dermatology group performs a case-control study to test whether indoor tanning is associated with melanoma. Cases are 260 adults aged 25–60 with newly diagnosed cutaneous melanoma from a cancer registry. Controls are 260 adults without melanoma recruited from orthopedic clinics, frequency-matched on age and sex. Exposure is assessed by interview about lifetime tanning bed sessions and sunburn history. Results: 48% of cases report indoor tanning vs 30% of controls. Investigators worry orthopedic clinic controls may have different outdoor activity patterns than the source population.
Which bias is most likely to affect the results of this study?
- Selection bias from nonrepresentative control recruitment (correct answer)
- Temporal bias because tanning occurs after melanoma
- Observer bias because pathology is not standardized
- Cross-contamination from controls receiving tanning exposure
- Confusion of terms between incidence and prevalence
Explanation: This question tests understanding of study design and evidence types in biostatistics and epidemiology. Study design involves choosing the appropriate methodology to answer a research question while minimizing bias. In this vignette, the described study design is a case-control study, which is appropriate for associating indoor tanning with melanoma. The correct answer identifies selection bias from nonrepresentative control recruitment as the main issue. A common misconception, as seen in choice B, is misidentifying the study design due to assuming temporal bias in retrospective exposure. Teaching strategies include emphasizing study design features and common biases, using real-world examples to illustrate abstract concepts, and practicing vignettes to identify design characteristics.
Question 10
A prospective cohort study enrolls 3,300 adults aged 35–70 without prior stroke from community clinics. Hypothesis: atrial fibrillation (AF) detected on wearable devices increases risk of ischemic stroke over 4 years. Exposure is AF episodes ≥30 seconds confirmed by patch monitor; outcomes are strokes confirmed by imaging and neurologist review. Results: stroke occurs in 52/600 (8.7%) with AF vs 96/2,700 (3.6%) without AF. Participants with AF are older and have more hypertension and diabetes. Investigators adjust for these factors but note some participants start anticoagulation after AF detection.
Which bias is most likely to affect the results of this study?
- Cross-contamination from anticoagulation affecting stroke risk (correct answer)
- Recall bias because AF is self-reported from memory
- Observer bias because stroke diagnosis is blinded
- Sample size error because large cohorts lack power
- Temporal bias because stroke occurs before AF detection
Explanation: This question tests understanding of study design and evidence types in biostatistics and epidemiology. Study design involves choosing the appropriate methodology to answer a research question while minimizing bias. In this vignette, the described study design is a prospective cohort study, which is appropriate for linking AF to stroke incidence over time. The correct answer identifies cross-contamination from anticoagulation affecting stroke risk as the bias. A common misconception, as seen in choice E, is misidentifying the study design due to confusing temporal bias in a prospective setup. Teaching strategies include emphasizing study design features and common biases, using real-world examples to illustrate abstract concepts, and practicing vignettes to identify design characteristics.
Question 11
A randomized controlled trial enrolls 260 adults aged 18–65 with acute uncomplicated cystitis. Hypothesis: a 3-day antibiotic regimen is non-inferior to a 5-day regimen for symptom resolution by day 7. Randomization is computer-generated; pills are identical, and patients and clinicians are blinded. Results: symptom resolution occurs in 88% (3-day) vs 90% (5-day); nausea occurs in 6% vs 10%. Investigators also track recurrence at 30 days and note similar follow-up completion in both groups.
Which of the following best describes the study design used in this scenario?
- Randomized, double-blind clinical trial comparing regimens (correct answer)
- Cross-sectional survey of antibiotic use and symptoms
- Case-control study selecting by symptom resolution status
- Prospective cohort study observing antibiotic duration choices
- Ecologic study comparing clinics by prescribing culture
Explanation: This question tests understanding of study design and evidence types in biostatistics and epidemiology. Study design involves choosing the appropriate methodology to answer a research question while minimizing bias. In this vignette, the described study design is a randomized, double-blind clinical trial, which is appropriate for evaluating the non-inferiority of a 3-day antibiotic regimen compared to a 5-day regimen in adults with acute uncomplicated cystitis. The correct answer identifies the study design's advantage, such as reducing selection bias and confounding through randomization and minimizing observer and participant bias via double-blinding. A common misconception, as seen in choice D, is misidentifying the study design due to its prospective nature, confusing it with a cohort study that lacks randomization and intervention. Teaching strategies include emphasizing study design features and common biases, using real-world examples to illustrate abstract concepts, and practicing vignettes to identify design characteristics.
Question 12
A case-control study evaluates whether occupational silica exposure is associated with rheumatoid arthritis (RA). Cases are 190 adults (70% women) with new RA diagnosis from rheumatology clinics. Controls are 190 adults without RA from the same health system, matched by age and sex. Exposure is determined by structured interview about past jobs and duration of dust exposure, aided by photographs of common workplace materials. Results: 34% of cases vs 20% of controls report silica exposure. Investigators note some participants struggle to recall jobs from decades earlier.
Which bias is most likely to affect the results of this study?
- Recall bias from inaccurate past exposure reporting (correct answer)
- Cross-contamination from cases switching to new jobs
- Observer bias because RA diagnosis is self-reported
- Temporal bias because exposure occurs after RA onset
- Sample size error because matching inflates bias
Explanation: This question tests understanding of study design and evidence types in biostatistics and epidemiology. Study design involves choosing the appropriate methodology to answer a research question while minimizing bias. In this vignette, the described study design is a case-control study, which is appropriate for associating silica exposure with rheumatoid arthritis. The correct answer identifies recall bias from inaccurate past exposure reporting as the main bias. A common misconception, as seen in choice D, is misidentifying the study design due to assuming temporal bias in retrospective assessment. Teaching strategies include emphasizing study design features and common biases, using real-world examples to illustrate abstract concepts, and practicing vignettes to identify design characteristics.
Question 13
Researchers conduct a case-control study of 300 adults aged 40–70 to test whether long-term proton pump inhibitor (PPI) use is associated with chronic kidney disease (CKD). Cases are 150 patients with newly diagnosed CKD (eGFR <60 for ≥3 months) identified from nephrology clinics. Controls are 150 patients from the same clinics with eGFR ≥90, frequency-matched on age and sex. Prior PPI exposure is obtained from electronic prescription records for the preceding 5 years. Results: 78/150 (52%) cases had ≥1 year of PPI prescriptions vs 54/150 (36%) controls. Investigators note that people referred to nephrology may differ from the general population.
Which of the following best represents the outcome of this study?
- Odds ratio comparing prior PPI use (correct answer)
- Risk ratio comparing CKD incidence over time
- Incidence rate of CKD per person-year
- Hazard ratio from survival analysis follow-up
- Prevalence difference of CKD at baseline
Explanation: This question tests understanding of study design and evidence types in biostatistics and epidemiology. Study design involves choosing the appropriate methodology to answer a research question while minimizing bias. In this vignette, the described study design is a case-control study, which is appropriate for assessing associations with chronic kidney disease using odds ratios. The correct answer identifies the odds ratio as the key measure comparing prior PPI use between cases and controls. A common misconception, as seen in choice B, is misidentifying the study design due to confusing it with prospective measures like risk ratios. Teaching strategies include emphasizing study design features and common biases, using real-world examples to illustrate abstract concepts, and practicing vignettes to identify design characteristics.
Question 14
A case-control study investigates whether prior concussions are associated with later diagnosis of migraine. Cases are 240 adults aged 18–50 with new migraine diagnosis from neurology clinics. Controls are 240 adults from the same clinics diagnosed with tension-type headache. Prior concussions are assessed by patient interview and review of sports medicine records when available. Results: 39% of migraine cases report ≥1 concussion vs 25% of controls. Investigators note that migraine patients may be more likely to remember head injuries.
Which statistical measure best represents the outcome of this study?
- Odds ratio for concussion history in cases (correct answer)
- Risk ratio for migraine incidence over follow-up
- Incidence rate of concussion per person-year
- Prevalence of migraine in the general population
- Hazard ratio for time to first migraine
Explanation: This question tests understanding of study design and evidence types in biostatistics and epidemiology. Study design involves choosing the appropriate methodology to answer a research question while minimizing bias. In this vignette, the described study design is a case-control study, which is appropriate for associating concussions with migraine using odds ratios. The correct answer identifies the odds ratio for concussion history in cases as the measure. A common misconception, as seen in choice B, is misidentifying the study design due to assuming prospective risk ratios. Teaching strategies include emphasizing study design features and common biases, using real-world examples to illustrate abstract concepts, and practicing vignettes to identify design characteristics.
Question 15
A city health department conducts a cross-sectional screening of 1,500 adults experiencing homelessness (ages 18–72; 22% women) during a 2-week outreach campaign. Hypothesis: untreated hypertension is common and associated with lack of a primary care clinician. Blood pressure is measured once; participants report whether they have a regular clinician and current medication use. Results: 41% meet hypertension criteria; among those without a regular clinician, 49% have hypertension versus 33% among those with one. Many participants report heavy alcohol use and limited sleep. Investigators describe the findings as a snapshot.
Which of the following best describes the study design used in this scenario?
- Cross-sectional study estimating prevalence at one time (correct answer)
- Prospective cohort study measuring incident hypertension
- Randomized trial assigning primary care access
- Case-control study selecting by hypertension status
- Case series describing only hypertensive participants
Explanation: This question tests understanding of study design and evidence types in biostatistics and epidemiology. Study design involves choosing the appropriate methodology to answer a research question while minimizing bias. In this vignette, the described study design is a cross-sectional study, which is appropriate for estimating hypertension prevalence among homeless adults. The correct answer identifies this as estimating prevalence at one time, capturing a snapshot. A common misconception, as seen in choice B, is misidentifying the study design due to confusing it with prospective incidence measurement. Teaching strategies include emphasizing study design features and common biases, using real-world examples to illustrate abstract concepts, and practicing vignettes to identify design characteristics.
Question 16
A randomized controlled trial in 360 adults aged 50–85 with symptomatic knee osteoarthritis tests whether an intra-articular biologic injection improves pain versus saline placebo at 12 weeks. Randomization is computer-generated; syringes are masked, and injectors are not involved in follow-up. Patients and outcome assessors are blinded. Primary outcome is change in WOMAC pain score; secondary outcome is rescue NSAID use. Results: clinically meaningful pain improvement occurs in 58% biologic vs 44% placebo; rescue NSAID use is lower (32% vs 41%). Investigators emphasize blinding to reduce expectation effects.
What is the primary advantage of the study design described?
- It measures exposure prevalence in a defined population
- It minimizes confounding via randomization and blinding (correct answer)
- It is ideal for rare diseases by selecting cases
- It eliminates all bias through perfect allocation
- It requires no follow-up and avoids attrition
Explanation: This question tests understanding of study design and evidence types in biostatistics and epidemiology. Study design involves choosing the appropriate methodology to answer a research question while minimizing bias. In this vignette, the described study design is a randomized controlled trial, which is appropriate for evaluating a biologic injection's effect on knee pain. The correct answer identifies the study design's advantage, such as minimizing confounding via randomization and blinding. A common misconception, as seen in choice C, is misidentifying the study design due to assuming it's ideal for rare diseases. Teaching strategies include emphasizing study design features and common biases, using real-world examples to illustrate abstract concepts, and practicing vignettes to identify design characteristics.
Question 17
A cross-sectional study evaluates 1,100 adults aged 50–80 at a community health fair to test whether hearing loss is associated with social isolation. Hearing is screened with audiometry; social isolation is measured with a validated questionnaire completed the same day. Results: 28% have moderate-to-severe hearing loss; high social isolation scores occur in 31% with hearing loss vs 18% without. Participants with hearing loss are older and have higher rates of diabetes. Investigators emphasize that both variables are measured concurrently.
Which of the following best represents the outcome of this study?
- Prevalence ratio of isolation by hearing status (correct answer)
- Odds ratio for future hearing loss incidence
- Risk ratio for isolation over longitudinal follow-up
- Hazard ratio for time to social isolation
- Relative risk reduction from randomized hearing aids
Explanation: This question tests understanding of study design and evidence types in biostatistics and epidemiology. Study design involves choosing the appropriate methodology to answer a research question while minimizing bias. In this vignette, the described study design is a cross-sectional study, which is appropriate for associating hearing loss with social isolation prevalence. The correct answer identifies the prevalence ratio of isolation by hearing status as the outcome. A common misconception, as seen in choice C, is misidentifying the study design due to assuming it measures longitudinal risk. Teaching strategies include emphasizing study design features and common biases, using real-world examples to illustrate abstract concepts, and practicing vignettes to identify design characteristics.
Question 18
A randomized controlled trial enrolls 520 adults aged 60–90 with osteoporosis and prior fragility fracture. Hypothesis: monthly injectable “osteo-mAb” reduces new vertebral fractures over 18 months compared with oral bisphosphonate. Randomization is 1:1; outcome assessors reading spinal imaging are blinded, but participants are not because routes differ. Results: new vertebral fracture occurs in 24/260 (9.2%) osteo-mAb vs 38/260 (14.6%) bisphosphonate. Adherence is higher in the injection group (92% vs 76%). Investigators suspect knowledge of assignment influences adherence and co-interventions.
Which bias is most likely to affect the results of this study?
- Performance bias from unblinded participants affecting adherence (correct answer)
- Recall bias because fractures are self-reported only
- Observer bias because imaging readers are unblinded
- Temporal bias because fractures precede randomization
- Generalization error because randomization ensures representativeness
Explanation: This question tests understanding of study design and evidence types in biostatistics and epidemiology. Study design involves choosing the appropriate methodology to answer a research question while minimizing bias. In this vignette, the described study design is a randomized controlled trial, which is appropriate for comparing treatments for osteoporosis fractures. The correct answer identifies performance bias from unblinded participants affecting adherence as the issue. A common misconception, as seen in choice D, is misidentifying the study design due to assuming temporal bias pre-randomization. Teaching strategies include emphasizing study design features and common biases, using real-world examples to illustrate abstract concepts, and practicing vignettes to identify design characteristics.
Question 19
A prospective cohort follows 2,200 adults aged 18–35 without nephrolithiasis to test whether high-dose vitamin C supplementation increases kidney stone incidence over 6 years. Supplement use is recorded annually and verified by purchase receipts when available. Incident kidney stones are confirmed by imaging reports. Results: stones occur in 3.2% of high-dose users vs 1.9% of nonusers. High-dose users also drink less water and consume more animal protein. Investigators adjust for diet but note hydration is hard to measure accurately.
Which bias is most likely to affect the results of this study?
- Confounding by diet and hydration behaviors (correct answer)
- Recall bias because stones change supplement reporting
- Observer bias because imaging reports are subjective
- Temporal bias because stones occur before supplementation
- Misclassification because exposure is randomized by investigators
Explanation: This question tests understanding of study design and evidence types in biostatistics and epidemiology. Study design involves choosing the appropriate methodology to answer a research question while minimizing bias. In this vignette, the described study design is a prospective cohort study, which is appropriate for linking vitamin C supplementation to kidney stone incidence. The correct answer identifies confounding by diet and hydration behaviors as the bias. A common misconception, as seen in choice B, is misidentifying the study design due to assuming recall bias in annual recordings. Teaching strategies include emphasizing study design features and common biases, using real-world examples to illustrate abstract concepts, and practicing vignettes to identify design characteristics.
Question 20
A public health team conducts a cross-sectional study in 1,200 adults aged 30–65 attending primary care visits in 1 month. They test the hypothesis that high sodium intake is associated with prevalent hypertension. Participants complete a 24-hour dietary recall, and blood pressure is measured once using an automated cuff. Hypertension is defined as BP ≥140/90 or current antihypertensive use. Results: 38% meet hypertension criteria; among those in the highest self-reported sodium quartile, 46% have hypertension versus 31% in the lowest quartile. Many participants also have obesity and chronic kidney disease, which correlate with both sodium intake and blood pressure. Investigators report an association but cannot determine which came first.
Which of the following best describes the study design used in this scenario?
- Prospective cohort study measuring incident hypertension
- Cross-sectional study assessing exposure and outcome simultaneously (correct answer)
- Randomized trial assigning sodium intake interventions
- Case-control study selecting by hypertension status
- Ecologic study comparing counties by salt sales
Explanation: This question tests understanding of study design and evidence types in biostatistics and epidemiology. Study design involves choosing the appropriate methodology to answer a research question while minimizing bias. In this vignette, the described study design is a cross-sectional study, which is appropriate for assessing associations between sodium intake and hypertension prevalence at a single time point. The correct answer identifies this as simultaneous measurement of exposure and outcome, highlighting its snapshot nature. A common misconception, as seen in choice A, is misidentifying the study design due to confusing it with prospective designs that track incidence. Teaching strategies include emphasizing study design features and common biases, using real-world examples to illustrate abstract concepts, and practicing vignettes to identify design characteristics.