If observational, what type of study design is this and how do you know

Question

A study was conducted. Medical records for 10,000 Medicare patients were examined. Researchers looked at whether or not patients had an hip or knee replacement between 2000 and 2010. They then looked at falls that occurred in the hospital within a week after those surgeries. 

 

1. Define the exposure and the outcome.
2. What is the research question? (Neutral!)
3. Is this an experimental or observational study? Explain how you know.
4. If observational, what type of study design is this and how do you know?
5. What biases might occur in this study? How might you avoid them?
6. What results might you expect?
7. If your results show an association between the exposure and the outcome, what other factors do you think need to be taken into consideration before you share these results?
8. What type of study would you suggest next to find stronger and/or additional evidence?

A study was conducted. Breast cancer patients with medium stage tumors were randomly assigned to two groups. One was asked to switch to a vegan diet while receiving treatment. The other group continued their usual diet. After 6 months, researchers compared the progress in tumor shrinkage between the two groups. 

 

1. Define the exposure and the outcome.
2. What is the research question? (Neutral!)
3. Is this an experimental or observational study? Explain how you know.
4. If observational, what type of study design is this and how do you know?
5. What biases might occur in this study? How might you avoid them?
6. What results might you expect?
7. If your results show an association between the exposure and the outcome, what other factors do you think need to be taken into consideration before you share these results?
8. What type of study would you suggest next to find stronger and/or additional evidence?

A study was conducted. Investigators are studying employees as a bus company. They measure the blood pressure of employees that work in the office and employees that drive buses.

 

1. Define the exposure and the outcome.
2. What is the research question? (Neutral!)
3. Is this an experimental or observational study? Explain how you know.
4. If observational, what type of study design is this and how do you know?
5. What biases might occur in this study? How might you avoid them?
6. What results might you expect?
7. If your results show an association between the exposure and the outcome, what other factors do you think need to be taken into consideration before you share these results?
8. What type of study would you suggest next to find stronger and/or additional evidence?

Answer 1

STUDY A
1	Exposure / Outcome	Exposure: Hip or knee replacement surgery (2000–2010) Outcome: Fall in hospital within 1 week post-surgery
2	Research Question	Among Medicare patients who underwent hip or knee replacement between 2000 and 2010, is there an association between the surgery and the occurrence of in-hospital falls within one week post-surgery?
3	Study Type	Observational – researchers did not assign surgery; they reviewed existing medical records.
4	Design	Retrospective Cohort How we know: • Population defined at baseline (Medicare patients 2000–2010) • Exposure (surgery) already occurred • Outcome (falls) measured after exposure using past records
5	Biases & Fixes	• Selection bias: Only Medicare patients → exclude non-Medicare Fix: Expand to all payers or stratify • Information bias: Falls under-reported in records Fix: Validate with incident reports • Confounding: Age, frailty, pre-op mobility Fix: Adjust via stratification or regression
6	Expected Results	Higher fall rate in surgery group (post-op mobility impairment, anesthesia effects, pain meds).
7	Before Sharing Results	• Confounders: Age, comorbidities, surgery type, hospital quality • Temporal ambiguity: Did fall cause re-admission (reverse causation)? • Generalizability: Medicare only (65+)?
8	Next Study	Prospective Cohort with standardized fall surveillance + mobility scoring pre/post-op.

STUDY B
1	Exposure / Outcome	Exposure: Switching to vegan diet during treatment Outcome: Tumor shrinkage after 6 months
2	Research Question	Among medium-stage breast cancer patients, does switching to a vegan diet during treatment affect tumor shrinkage after 6 months compared to continuing usual diet?
3	Study Type	Experimental – random assignment to diet groups.
4	Design	N/A (not observational)
5	Biases & Fixes	• Compliance bias: Vegan group may not adhere Fix: Diet logs + biomarkers (e.g., fiber intake) • Attrition bias: Dropouts differ by diet tolerance Fix: Intention-to-treat analysis • Measurement bias: Tumor size via different imaging Fix: Blinded radiologist review
6	Expected Results	Uncertain – possible modest benefit from anti-inflammatory plant compounds, but no strong prior evidence.
7	Before Sharing Results	• Adherence levels • Baseline tumor biology (ER/PR status) • Concurrent treatments (chemo, radiation) • Sample size (power to detect difference)
8	Next Study	Multi-center RCT with longer follow-up (2–5 yrs) + recurrence-free survival endpoint.

STUDY C
1	Exposure / Outcome	Exposure: Job type (office worker vs. bus driver) Outcome: Blood pressure (measured at one time point)
2	Research Question	Among bus company employees, is there a difference in blood pressure between office workers and bus drivers?
3	Study Type	Observational – no intervention; exposure (job) already exists.
4	Design	Cross-Sectional How we know: • Exposure and outcome measured at the same time • No follow-up period
5	Biases & Fixes	• Healthy worker effect: Drivers may be healthier to pass CDL Fix: Compare to general population • Measurement bias: BP taken once, white-coat effect Fix: Average 3 readings, standardized protocol • Confounding: Age, BMI, stress, shift work Fix: Match or adjust
6	Expected Results	Higher BP in drivers (stress, sedentary driving, irregular shifts).
7	Before Sharing Results	• Temporality: Which came first – job or high BP? • Confounders: Smoking, diet, exercise • Selection: Only current employees (survivor bias)
8	Next Study	Prospective Cohort: Measure BP at hiring → follow both groups over 5 years.