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A study examines whether a new blood biomarker predicts depression risk. Consider two measurement scenarios:
Scenario 1: The test has systematic error—it reads 20% higher for ALL individuals, regardless of depression status. (Non-differential error)
Scenario 2: The test is accurate (±5%) for non-depressed people but reads 40% higher for depressed people. (Differential error—depends on outcome)
Which scenario presents a greater threat to validity?
A study examines whether a new blood biomarker predicts depression risk. Consider two measurement scenarios:
Scenario 1: The test has systematic error—it reads 20% higher for ALL individuals, regardless of depression status. (Non-differential error)
Scenario 2: The test is accurate (±5%) for non-depressed people but reads 40% higher for depressed people. (Differential error—depends on outcome)
Which scenario presents a greater threat to validity?