**** A community consists of 500 individuals, and over a period of 2 years, 20 new cases of a certain disease were identified. The total observation time amounted to 950 person-years. What is the incidence rate of this disease in the population?

1. A

   2.1 per 1000 person-years

2. B

   2.1 per 100 person-years

3. C

   4 per 1000 person-years

4. D

   2 per 100 person-years

Appeared in: AIIMS Nagpur NO- 2020

Explanation

• The incidence rate is calculated by dividing the number of new cases by the total person-time at risk.
• In this problem, there are 20 new cases and 950 person-years of observation.
• The calculation is (20 new cases / 950 person-years) = 0.02105.
• To express this rate per 100 person-years, the result is multiplied by 100: 0.02105 * 100 = 2.105, which is approximately 2.1 per 100 person-years.

Why Other Options Were Wrong

• Option A: This option incorrectly uses a multiplier of 1000. The calculated rate per 1000 person-years would be (20 / 950) * 1000 = 21.1, not 2.1.
• Option C: This value is incorrect. It may result from an erroneous calculation, possibly by incorrectly using the total population size (500) instead of the person-years. For example, (20/500)*100 = 4 per 100 people over 2 years, not an incidence rate per person-years.
• Option D: This is an inaccurate rounding of the correct answer. The calculated value is 2.105, which is more precisely represented as 2.1 rather than rounding down to 2.

Related Visual

Clinical Relevance

• Nursing practice connection: Knowing Calculation of Incidence Rate (Incidence Density) helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
• Understanding how to calculate and interpret incidence rates is a fundamental skill for community health nurses and public health professionals.
• Incidence rates help nurses identify disease trends, assess the risk of developing a disease in a population, and evaluate the effectiveness of public health interventions and prevention programs.
• For example, a sudden increase in the incidence rate of influenza in a community would signal to nurses the start of an outbreak, prompting actions like promoting vaccination, educating the public on hygiene, and preparing healthcare facilities.

How to Approach the Question

• First, identify the key pieces of information given in the question: the number of new cases and the total person-time of observation.
• Recall the formula for calculating the incidence rate (also known as incidence density): Incidence Rate = (Number of New Cases) / (Total Person-Time).
• Substitute the given values into the formula: 20 new cases / 950 person-years.
• Perform the division to get the rate per single person-year.
• Examine the options to see the required format (e.g., per 100 or per 1000 person-years).
• Multiply your calculated rate by the appropriate factor (100 or 1000) to match the format of the options and select the one that corresponds to your result.

Concept Tested & Keywords

• Concept Tested: Calculation of Incidence Rate (Incidence Density)
• Stem keywords: community, incidence rate, new cases, person-years
• Lead-in keywords: What is
• Clinical cues: The care setting changes urgency, monitoring level, and the expected nursing action.

Question ID

QISoe2yk6vas5kqu958NxJ

Copy ID

Reference Book

E6 Parks TextBook of Preventive & Social Medicine part 1 — Subpart A (pp 26-201 of 604) p. 53-55

E6 NursingResearch Suresh Sharma 5e Part 2 p. 198-200