In a cohort study, 10 industrial workers are followed for development of noise-induced hearing loss. Three are followed for 10 years each, four for 8 years each, two for 6 years each, and one for 5 years. Two workers develop hearing loss during follow-up. What is the incidence density?

• A 20 per 100 person-years
• B 25.3 per 100 person-years ✓
• C 2.53 per 100 person-years
• D 33 per 100 person-years

Explanation

Total observation time is (3 x 10) + (4 x 8) + (2 x 6) + (1 x 5) = 30 + 32 + 12 + 5 = 79 person-years. Incidence density = 2 cases / 79 person-years = 0.0253, expressed as 25.3 per 1000 person-years or equivalently 2.53 per 100 person-years. Wait: 0.0253 per person-year equals 2.53 per 100 person-years, so option C states the correct figure. The key is C.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.