In a given population of 10000, there were 30 cases of diabetes already present on 01/01/2025 and in the year 2025, 400 more cases developed diabetes. But 10 cases of diabetes died in the year 2025, i.e., before 31/12/2025. Which one of the following statements is correct regarding the disease situation?
The period prevalence of diabetes in 2025 was 43/1000.
The correct answer is "The period prevalence of diabetes in 2025 was 43/1000". Period prevalence counts everyone who had the disease at any time during the period — cases present at the start plus all new cases, including those who die during it. Here 30 old cases + 400 new cases = 430 cases among 10000, so period prevalence = 430 ÷ 10000 = 43 per 1000.
Why the others are wrong: Incidence 42/1000 is wrong — incidence counts only new cases over the population at risk: 400 ÷ (10000 − 30) = 400/9970, roughly 40 per 1000 per year. Point prevalence on 31/12/2025 of 43/1000 is wrong because 10 cases died, leaving 430 − 10 = 420 survivors, i.e. 42 per 1000. Prevalence of 44/1000 would need 440 cases, a figure not derivable from the data.
Key point: Prevalence = old + new cases (a snapshot); incidence = new cases only over the population at risk (a rate per unit time). Prevalence = Incidence × mean Duration, which is why chronic diseases like diabetes accumulate high prevalence.
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Important Questions from Biostatistics
What is the specificity of sputum microscopy in detection of Pulmonary Tuberculosis (PTB) as per the information given below?
PTB Total Sputum microscopy Present Absent Positive 270 20 290 Negative 30 180 210 Total 300 200 500 In a cohort of 500 women attending antenatal clinic, 70 % had ultrasonography (USG). This cohort was followed up at delivery. Of the women who had USG, 70 delivered low birth weight (LBW) babies; whereas of the women, who did not undergo USG, 50 delivered LBW babies. The incidence of LBW babies among women who had USG is:
In a case-control study, 300 women aged 20-45 years suffering from breast cancer were compared with age-matched 300 women without breast cancer. It was observed that 120 women among cases and 60 women among controls were obese. The odds ratio of developing breast cancer among obese women is:
What is the relative risk of developing pulmonary embolism in users of oral contraceptives as per the information given below?
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