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Descriptive Epidemiology, Measures of Disease Frequency

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Principles of Epidemiology

Homework Assignment #1

*Descriptive epidemiology, Measures of disease frequency*

NOTE: Assignment is due (hard-copy and typed) at the start of the discussion group.

  1. Create a summary table of formulas that will be helpful for you from this week’s lectures.

CI=

Number of new cases of disease during a specified time period

Number in at-risk population at beginning of time period

AR=

Number of new cases of disease

Total population at risk for a ‘limited’ period of observation

Case-fatality rate=

Number of deaths from disease

Number of cases of that disease

IR=

Number of new cases of disease during a specified time period

Total at-risk person time of obervation

MR=

Total number of deaths

Total person-time of follow-up

P=

Number of existing cases of disease at a specified time

Total of people in population at that time

Birth defect rate=

Number of children born with defects

Total number of births

  1. A total of 2,121,323 deaths were recorded in the US in 1987.  The mid-year population was estimated to be 243,401,000.  HIV-related mortality and population data by age for all residents and for black males are shown in the table below, also for 1987.  Use these data to calculate the following:
  1. Crude mortality rate for the US population

MR=2,121,323/243,401,000=871.5 per 100,000 PY  

  1. Express this crude mortality rate (your answer to part a.) in a different way.  What is this measure called?

One-year Cumulative Incidence of death=0.87%

  1. HIV-specific mortality rate for entire population

MR=13,465/243,401,000=5.5 per 100,000 PY

  1. HIV-specific mortality rate among all 35-44 year olds

MR=4794/34,305,000=14.0 per 100,000 PY

  1. HIV-specific mortality rate among 35-44 year old black males

MR=1212/1,663,000=72.9 per 100,000 PY

  1. Summarize your results in a couple of sentences.

HIV mortality rate for entire population of US in 1987 was 5.5 per 100,000PY. Important differences were observed, with black males among 35-44 years of age suffering higher HIV deaths than that of others

All races

Black males

Age group

HIV deaths

Population

HIV deaths

Population

0-4

191

18,252,000

47

1,393,000

5-14

47

34,146,000

7

2,697,000

15-24

492

38,252,000

145

2,740,000

25-34

5026

43,315,000

1326

2,549,000

35-44

4794

34,305,000

1212

1,663,000

45-54

1838

23,276,000

395

1,117,000

55+

1077

51,855,000

168

1,945,000

  1. The following 8 elderly women were residents of an assisted living facility and were followed by the same doctor for 12 years.  The table below describes events that occurred during the 12-year period.  

Patient

Outcome

A

Followed for the full 12 years.  At the end of year 5, she was diagnosed with Alzheimer’s disease.

B

Died at the end of year 2 and never had Alzheimer’s disease.

C

Died at the end of year 8 and never had Alzheimer’s disease.

D

Diagnosed with Alzheimer’s disease at the end of year 2 and died at the end of year 8.

E

Lost to follow-up at the end of year 7 and never had Alzheimer’s disease.

F

Died at the end of year 4.  At the start of the study, she had already had Alzheimer’s disease for 2 years.

G

Lost to follow up at the end of year 9.  At the end of year 3, she was diagnosed with Alzheimer’s disease.

H

Followed for the full 12 years, and never had Alzheimer’s disease.

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