The figure on page 3 shows data from a 5 year hypothetical prospective cohort st
ID: 122693 • Letter: T
Question
The figure on page 3 shows data from a 5 year hypothetical prospective cohort study. Each line summarizes the experience of a person in the study; the exposure was present for 15 individuals (ID numbers 1-15) and the other 15 people were non-exposed (ID# 16-30). All individuals were free of the disease at baseline, and incident cases of disease were diagnosed at mid-year or at examinations conducted at the end of each year. Answer the following questions using the data displayed in the figure.
1 Based on the data from the first two years of the study, answer the following questions.
1a. Compute and interpret the cumulative incidence of disease separately for the exposed and the non-exposed for the first 2 years of the study (i.e. years 1 and 2 combined). (4 points for calculation and 2 points for interpretation)
lb. Compute the incidence odds (odds of cumulative incidence ) for each exposure group for the first 2 years in the study. Is the incidence odds a good estimate of the cumulative incidence computed in 1a? (4 points for calculation and 2 points for interpretation)
1c. Compute and interpret the prevalence of disease for each exposure group at the examination at the end of year 2. Briefly discuss why the prevalence measures are similar or different to the incidence measures in 1a. (4 points for calculation and 2 points for interpretation, 2 points for discussion)
1d. Compute and interpret the incidence rate (density) for each exposure group using the first 2 years of data. (4 points for calculation and 2 points for interpretation)
2. Compute cumulative incidence and incidence rate (density) of
disease for each exposure group using the first 3 years of data. Compute the prevalence of disease for each exposure group at the examination at the end of year 3. Briefly discuss the comparison of cumulative incidence and prevalence (as in 1c). (12 points for calculation, 2 points for discussion)
3. Compute cumulative incidence and incidence rate (density) of
disease for each exposure group using the first 4 years of data. Compute the prevalence of disease for each exposure group at the examination at the end of year 4. Describe how loss to follow-up affects each of these measures. (12 points for calculation, 2 points for discussion)
4. Compute the incidence rate (density) for each exposure group using all five years of data. (4 points for calculation)
5. Describe the differences between cumulative incidence and incidence rate (density) with respect to their (1) units, (2) ranges, and (3) characteristics of populations for which these measures are appropriate for. (3 points)
EXPOSED
ID #
1 ---------1---------2---------3---------4---------5
2 ---------1---------2---------3---------4-----xxxxx
3 ---------l-----xxxxxxxxxxD
4 ---------1---------2---------3---------4---------5
5 ---------1---------2---------3---------4---------5
6 ---------1---------2---------3---------4---------5
7 -----xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
8 ---------1---------2---------3---------4---------5
9 ---------1---------2---------3---------4---------5
10 ---------l-----xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
11 -----xxxxxxxxxxxxxxxxxxxxD
12 ---------1---------2---------3---------4-----L
13 ---------1---------2---------3---------4---------5
14 ---------1---------2---------3---------4---------5
15 ---------1---------2---------3---------4---------x
YEAR OF STUDY
NON-EXPOSED
ID #
16 ---------l-----xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
17 ---------1---------2---------3-----L
18 ---------1---------2---------3---------4---------5
19 ---------1---------2-----xxxxxxxxxxxxxxxxxxxxxxxxx
20 ---------1---------2---------3---------4---------5
21 ---------1---------2---------3-----L
22 ---------1---------2---------3---------4---------5
23 ---------1---------2---------3---------4---------x
24 ---------1---------2---------3---------4---------5
25 ---------1---------2---------3---------4---------x
26 ---------1---------2---------xxxxxxxxxxxxxxxxD
27 ---------1---------2---------3---------4---------5
28 ---------1---------2---------3---------4---------5
29 ---------1---------2---------3---------4---------5
30 ---------1---------2---------3---------4---------5
YEAR OF STUDY
* 1 represents the examination at the end of year 1, 2 represents the examination at year 2, etc. When disease is diagnosed at the examination the letter "x" appears instead of the number" (e.g., the person with ID# 26 was diagnosed at the end of year 3). A blank space indicates that the person was not present at the examination.
LEGEND FOR THIS FIGURE:
------ ACTIVE IN STUDY, AT RISK
xxxxxx ACTIVE IN STUDY, DISEASED
L LOST TO FOLLOW-UP
D DIED
Note to chegg expert: This is Public Health (Epidemiology problems), please provide step by step solution and try to finish it as soon as possible. Thanks so much!
Explanation / Answer
1Ans:
1a:- Cumulative incidence for exposed:
Formulae: Number of new diseased in 1-2yrs
No. of participants in 1-2yrs.
CI: 4/15 =0.26% in 2yrs
Cumulative incidence for Non exposed :
Formulae: Number of new diseased in 1-2yrr/No. of participants in 1-2yrs.
CI: 1/15 = 0.06% in 2yrs
** 0.26% of the people identified as diseased in first 2yrs in exposed group
**0.06% of the people identified as diseased in first 2yrs in non –exposed group
1b:-
A disease-odds ratio is the ratio of the odds of having the disease among the exposed and the odds of having the disease among the unexposed
Developing the disease
Not developing the disease
Total
Exposed
A(4)
B(11)
a+b(4+11)
Not exposed
C(1)
D(14)
c+d (1+14)
Total
5
25
30
For both exposed and non exposed
Risk of disease p = 5 / 30 = 0.166%
Odds of disease = p/1-p (5/ 30) / 1 – (5/30) = 0.2%
Odd ratio for exposed
Risk ratio P = 4/15 =0.2
Odds of disease = p/1-p
= (4/15)/1-(4/15)
= (4/15)/(11/15), =4*15/11*15
=4/11 =0.36
Odd ratio for Non-exposed
Risk ratio P = 1/15 =0.06
Odds of disease = p/1-p
= (1/15)/1-(1/15)
= (1/15)/(14/15), =1*15/14*15
=1/14 =0.07
1cAns:
Prevalence is a term which is used to denote the measurements of disease frequency. Prevalence of a disease is the proportion of population affected by a specific disease at a particular time
For Exposed
All new & preexisting cases of specific disease (n) = 4
Total population = 15
To find, Prevalence Rate of Disease
Solution:
Prevalence Rate of Disease = (n / Total population) x 10 n
= (4/ 15) x 10 4
= 0.26667 x 10000
= 2666.7
For non exposed
All new & preexisting cases of specific disease (n) = 1
Total population = 15
To find,
Prevalence Rate of Disease
Solution:
Prevalence Rate of Disease = (n / Total population) x 10 n
= (1 / 15) x 10 1
= 0.06667x 10
= 0.6
1dANS:
Incidence proportion is a measure of the risk of disease or the probability of developing the disease during the specified period
Incidence rate = Total no. of new cases/Total population at risk
Exposed = 4/11 = 0.36 %
Non exposed = 1/14 = 0.07%
2Ans:
For exposed :
CI: Number of new diseased in 1-3yrr/No. of participants in 1-3yrs.
= 2/13 =0.15%
** 0.15% of the people identified as diseased in first 3yrs in exposed group (Total population decreased to 13 due to 2peopl’s death)
Prevalence: Prevalence Rate of Disease = (n / Total population) x 10 n
=(2/13)*102
= 0.15 *100
= 15
Incidence rate = Total no. of new cases/Total population at risk
=2/11 =0.181
For Non Exposed
CI: Number of new diseased in 1-3yrr/No. of participants in 1-3yrs.
= 3/15 = 0.2%
**0.2% of the people identified as diseased in first 3yrs in non –exposed group
Prevalence Rate of Disease = (n / Total population) x 10 n
=(3/15)*103
=0.2*1000
=200
Incidence rate = Total no. of new cases/Total population at risk
=3/12 = 0.25
3Ans.
For exposed :
CI: Number of new diseased in 1-4yrr/No. of participants in 1-4yrs.
= 2/13 =0.15%
** 0.15% of the people identified as diseased in first 3yrs in exposed group (Total population decreased to 13 due to 2peopl’s death)
Prevalence: Prevalence Rate of Disease = (n / Total population) x 10 n
=(2/13)*102
= 0.15 *100
= 15
Incidence rate = Total no. of new cases/Total population at risk
=2/11 =0.181
Therese no loss cases for the follow up here but died 2 people drop in population participation lead to the rate of risk is increased among population
For Non Exposed
CI: Number of new diseased in 1-4yrr/No. of participants in 1-4yrs.
= 3/12= 0.25%
**0.25% of the people identified as diseased in first 3yrs in non –exposed group
Prevalence Rate of Disease = (n / Total population) x 10 n
=(3/12)*103
=0.25*1000
=250
Incidence rate = Total no. of new cases/Total population at risk
=3/09 = 0.33%
4Ans:
Exposed Incidence rate = Total no. of new cases/Total population at risk
=4/12 = 0.33 (Total population has come down to 12 due to death and loss of visit)
Non Exposed Incidence rate = Total no. of new cases/Total population at risk
=3/12 = 0.25 (Total population has come down to 12 due to death and loss of visit)
5Ans:
Cumulative incidence calculate the risk of new disease cases among the total participants in a given period of time whereas incident risk calculates with the new cases divided by total cases –risk cases. The probability that the patient will get the disease within the time-frame is noted by cumulative. CI characterizes individuals, thus measuring their transition from health to disease. The incidence rate is the number of new cases per population at risk in a given time period.
Developing the disease
Not developing the disease
Total
Exposed
A(4)
B(11)
a+b(4+11)
Not exposed
C(1)
D(14)
c+d (1+14)
Total
5
25
30