Question

) A researcher recruited 2100 men in his research and followed up every year for 4 years to find out the incidence rate of respiratory disease.

After 1 year, there was not a new diagnosis of respiratory disease, and 100 lost to follow up,

After 2 years, found one new case of respiratory disease and 99 lost to follow up,

After 3 years, found 7 new cases of respiratory diseases and seven hundred ninety three lost to follow up.

After 4 years, found eight new cases of respiratory diseases and three hundred ninety two lost to follow up.

Calculate the incidence rate of respiratory disease

(**new cases of respiratory disease and men lost to follow up were disease-free for six months) ** and contribute ½ years to the denominator)

Answer 1

Incidence rate of respiratory disease = Total number of new cases of respiratory diseases / Total population at risk

After 1 year, there was not a new diagnosis of respiratory disease, and 100 lost to follow up -

New cases and population lost to follow up = 0 + 100 = 100

Remaining population at risk after 1 year = 2100 - 100 = 2000

Contribution to numerator = New case = 0

Contribution to denominator = 100 * 0.5 = 50

After 2 years, found one new case of respiratory disease and 99 lost to follow up -

New cases and population lost to follow up = 1 + 99 = 100

Remaining population at risk after 2 years = 2000 - 100 = 1900

Contribution to numerator = New cases = 1

Contribution to denominator = 100 * 1.5 = 150

After 3 years, found 7 new cases of respiratory diseases and seven hundred ninety three lost to follow up -

New cases and population lost to follow up = 7 + 793 = 800

Remaining population at risk after 3 years = 1900 - 800 = 1100

Contribution to numerator = New Cases = 7

Contribution to denominator = 800 * 2.5 = 2000

After 4 years, found eight new cases of respiratory diseases and three hundred ninety two lost to follow up -

New cases and population lost to follow up = 8 + 392 = 400

Remaining population at risk after 4 years = 1100 - 400 = 700

Contribution to numerator = New Cases = 8

Contribution to denominator = 400 * 3.5 = 1400

Remaining population at risk after 4 years = 700 => Contribution to denominator = 700 * 4 = 2800

Incidence rate of respiratory disease = Total number of new cases of respiratory diseases / Total population at risk

= (0 + 1 + 7 + 8) / (50 + 150 + 2000 + 1400 + 2800)

= 16 / 6400

= 0.0025 Cases per Person-Year