What will be the incidence rate, if there are 500 new cases of an illness in a population of 30,000 in a year?

Appeared in: ESIC Nursing Officer-7July 2024

Explanation

The incidence rate measures the occurrence of new cases of a disease in a population over a specified time.
The formula is: (Number of new cases / Total population at risk) × Multiplier.
Using the given data: (500 / 30,000) = 0.01667.
To express this per 1000 people, multiply by 1000: 0.01667 × 1000 = 16.67.
Rounding to one decimal place gives 16.7 per 1000 per year, which matches the correct option.

Option A: The value 1.42 does not result from any logical calculation using the provided numbers. It is a significant miscalculation.
Option B: The value 14.2 is an incorrect calculation. It may result from a transcription error or a mistake in the division or multiplication step.
Option D: This is a common decimal placement error. It results from dividing 500 by 30,000 (0.01667) and then multiplying by 100 instead of 1000, yielding 1.67.

Visual 1: Flowchart: Step-by-step guide to calculating incidence rate, showing the formula and where to plug in the numbers.
Visual 2: Infographic: A visual comparison of Incidence vs. Prevalence. Incidence is depicted as new raindrops falling into a bucket, while prevalence is the total amount of water in the bucket at one time.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Calculation of incidence rate in epidemiology as background academic context rather than a clinical decision trigger.
Community health nurses use incidence rates to identify disease outbreaks, assess the effectiveness of prevention programs, and allocate resources.
Understanding these rates helps nurses educate patients and communities about health risks and preventive measures.
What if the question asked for the prevalence rate? The answer could not be determined. Prevalence requires knowing the total number of existing cases (both old and new), not just the new cases that occurred during the year.

How to Approach the Question

Identify the key term in the question: 'incidence rate'.
Recall the standard formula for incidence rate: (New Cases / Population at Risk) × Multiplier.
Extract the necessary values from the question: New Cases = 500, Population = 30,000.
Check the options to determine the multiplier. The options are 'per 1000', so the multiplier is 1000.
Substitute the values into the formula: (500 / 30,000) × 1000.
Perform the calculation and compare the result (16.67) to the given options to find the closest match.

Concept Tested & Keywords

QGuV29miBCelDY7pAmM_Ic

Practise the full ESIC Nursing Officer-7July 2024

Attempt every question from this paper in a timed mock, then review the full solution for each one.