Biostatistics & Study Design USMLE Step 1 Practice Question
A 42-year-old woman with obesity (BMI 34 kg/m²) presents for metabolic evaluation. Vital signs: BP 138/82 mmHg, HR 88 bpm, RR 14/min, temp 37°C. Fasting insulin is 18 mIU/L. Researchers perform simple linear regression modeling weekly exercise hours versus fasting insulin across 85 obese adults. The residual plot demonstrates a clear U-shaped pattern rather than random scatter around zero. HbA1c is normal at 5.2%. Which conclusion is most appropriate regarding model assumptions?
Answer choices
- AThe linearity assumption is likely violatedCorrect answer
- BThe outcome must be categorical
- CThe sample size is too large
- DThere is complete absence of confounding
- EThe model has perfect calibration
- FThe relationship between exercise and fasting insulin follows a normal distribution
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