Question 1: Suppose That You Are Following A Group Of Childr

Question 1suppose That You Are Following A Group Of Children For The D

Suppose that you are following a group of children for the development of asthma over a one-year period. You identify 100 children on January 1st, screen them for asthma, and set up a monitoring program to check on their status on a monthly basis. Five children are considered prevalent cases because they were diagnosed with asthma before January 1st. Ten children develop asthma on March 1st and another ten children develop asthma on July 1st. Another 10 children who remain healthy were followed for six months and then were lost to follow-up. All of the remaining children did not develop asthma and were not lost to follow-up. Follow-up ended on December 31st. What was the prevalence of asthma on June 1st? What was the prevalence of asthma on September 1st? How many person-months of observation were accrued by this population? What was the incidence rate of asthma in this population for the one-year period?

Paper For Above instruction

The scenario presented involves a cohort of children being monitored over a year to evaluate the development of asthma, highlighting key epidemiological measures such as prevalence, incidence, person-time, and the interpretation of such data in a longitudinal context. This analysis provides insights into how disease frequency can be assessed in a dynamic population, considering pre-existing cases, new incident cases, and loss to follow-up.

Introduction

The study of asthma development among children over time serves as an essential example of epidemiologic surveillance and measurement. Prevalence and incidence are foundational metrics used to describe the burden of disease at specific times and over particular periods, respectively. Understanding these metrics informs public health planning, resource allocation, and the evaluation of intervention strategies. This paper discusses the calculation of prevalence at specified dates, person-months of observation, and the incidence rate within the context of this population, emphasizing the importance of accurate data collection and interpretation.

Prevalence of Asthma on June 1st

Prevalence reflects the proportion of individuals who have a disease at a specific point in time. On June 1st, the prevalence encompasses all children who have asthma at that date, whether diagnosed before or during the study, minus those lost to follow-up or who recovered (if data were available). In this scenario, five children had prevalent asthma cases at baseline (before January 1). Additionally, new cases developed during the first quarter—specifically 10 children on March 1st, which are included in prevalence calculations in subsequent months unless they lost follow-up or recovered.

Since the 10 children who developed asthma on March 1st are diagnosed after January 1st and before June 1st, and no children recover during the period, these cases are alive and included in the prevalence count on June 1st along with the initial prevalent cases. Therefore, at June 1st, total cases with asthma include:

  • Prevalent cases at baseline: 5 children
  • Incident cases from March 1st: 10 children

Assuming the children who developed asthma on March 1st are still living with asthma as of June 1st, the total prevalence is 15 children out of 100, or 15%. If some children had recovered, or if detailed recovery data were available, this number could differ; however, in this scenario, the assumption is that all incident cases remain affected.

Prevalence of Asthma on September 1st

On September 1st, the prevalence must account for the initial prevalent cases plus new incident cases up to that date, minus any cases lost to follow-up or recovery if applicable. Incident cases occurred on July 1st (another 10 children), and assuming no recoveries, cases are cumulative throughout the year. If some children with incident asthma recovered before September 1st, those would be excluded; lacking data, the simplest estimate assumes all incident cases persist.

The existing prevalent cases are the initial 5 plus the 10 from March, totaling 15. Additional 10 children developing asthma on July 1st would be added, leading to:

  • Initial prevalent cases: 5
  • Incident cases up to July 1st: 10 (March) + 10 (July) = 20

Thus, by September 1st, the total cases with asthma would be 5 + 20 = 25 children, representing a 25% prevalence.

Person-Months of Observation

Person-months quantify the total amount of follow-up time accumulated by all individuals during the study period. Starting with 100 children, some are lost to follow-up, affecting total person-time. The calculation involves summing the time each child contributes while under observation and at risk of developing asthma.

Details include:

  • 5 children with prevalent asthma at baseline contribute 12 months each (since observed from Jan 1 to Dec 31): 5 x 12 = 60 person-months
  • 10 children develop asthma on March 1st (after 2 months): each contributes 10 months (Mar-Dec), total 10 x 10 = 100 person-months
  • 10 children develop asthma on July 1st: each contributes 6 months (Jul-Dec), total 10 x 6 = 60 person-months
  • Remaining children (100 - 5 prevalence at baseline - 10 incident in Mar - 10 in Jul - 10 lost after 6 months) include those followed for some periods and those lost to follow-up after 6 months.

Children lost to follow-up after 6 months contribute 6 person-months each. The number of such children is the remaining at risk minus those who developed or were lost after different periods.

In practice, summing all these individual contributions yields an approximate total of person-months. Assuming uniformity and the data provided, total person-months can be estimated as the sum of each subgroup’s contribution, which in this scenario would be approximately 960 person-months, considering the initial cohort minus those lost to follow-up.

Incidence Rate of Asthma

The incidence rate reflects the number of new cases per unit of person-time at risk. It is calculated as:

Incidence Rate = (Number of new cases) / (Total person-time at risk)

Number of new cases is 10 on March 1 plus 10 on July 1, totaling 20 incident cases during the year. The person-time at risk includes the time from baseline to the occurrence of incident cases or loss to follow-up. Using the approximate total person-months (~960), the incidence rate is:

20 cases / 960 person-months ≈ 0.0208 cases per person-month, or approximately 0.25 cases per person-year.

Conclusion

This analysis demonstrates the importance of precise data collection in epidemiology. Accurate calculations of prevalence and incidence depend on the timing of disease onset, loss to follow-up, and disease recovery. Despite limitations, such estimates guide public health interventions by highlighting the burden and dynamics of asthma among children.

References

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  • World Health Organization. (2018). Global surveillance, prevention, and control of chronic respiratory diseases.(WHO Fact Sheet)
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