A cohort of 1,000 adults free of diabetes is followed with annual visits for 5 years. Fifty develop type 2 diabetes at their final annual visit, contributing 5 years each. One hundred participants are lost to follow-up at exactly 2 years. The incidence density of diabetes is:

• A 5.0 per 1,000 person-years
• B 10.0 per 1,000 person-years
• C 11.2 per 1,000 person-years ✓
• D 16.7 per 1,000 person-years

Explanation

Person-time is calculated as 850 completers multiplied by 5 years, equal to 4,250 person-years, plus 100 dropouts multiplied by 2 years, equal to 200 person-years, totalling 4,450 person-years. Incidence density is 50 divided by 4,450, which is 0.0112 per person-year or 11.2 per 1,000 person-years. Using the initial denominator of 1,000 over 5 years gives 10.0 per 1,000, which ignores censoring of losses and overstates the denominator.

Reference: Gordis Epidemiology, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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