Download WEEK5- ASSINGMENTM_ Cigarette Smoking and Lung Cancer

Zahra Abdalla
MPH 510 – Applied Epidemiology
Dr. Boye
Cigarette Smoking and Lung Cancer
Question 1: What makes the first study a case-control study?
The first study is a case-control participants are selected based on the disease and individual with
the disease are compares individuals without the disease. In this study patients diagnosed with
the lung cancer and the patients of other disorders and without the disease were included in the
study. Also according to Friis and Sellers (2014), case-control study uses one point observation
(hospital) which is mention in this study.
Question 2: What makes the second study a cohort study?
The second study is cohort study because the study was followed over period of time. In this
study individual’s information about past smoking behaviors were obtained from different
sources and time.
Question 3: Why might hospitals have been chosen as the setting for this study?
CDC / EIS Summer Course 2003: Smoking and Lung Ca - Student's Guide Page 3
Using a hospital setting for case -control study for one observation area ensure accuracy. In this
study it was perhaps easy to track patients information, and easy to recall exposures.
Question 4: What other sources of cases and controls might have been used?
As stated by Friis and Sellers,(2014), other sources that is helpful for cases and controls are a
disease registry, Medical records, and disease statistics. I would like think other sources that
could have been is using other population such as older adults who are in nursing homes.
Question 5: What are the advantages of selecting controls from the same hospitals as cases?
The advantages selecting controls from the same hospitals as cases could mean that the
individuals are easy to locate. Also since they are based on one location there is time saving and
cost effective to track the individual’s medical records.
Question 6: How representative of all persons with lung cancer are hospitalized patients with lung
cancer?
It is difficult to say hospitalized patients with lung cancer was probably representative of
all persons with lung cancer. Because not all patients with who are hospitalized with lung cancer
represent all cases in the general population.
Question 7: How representative of the general population without lung cancer are hospitalized
patients without lung cancer?
Hospitalized patients without lung cancer could mean they have other health conditions than
those of the general population. At the same time it is difficult to state how much of date
hospitalized patients without lung cancer represent or similar to patient general population
without lung cancer.
Question 8: How may these representativeness issues affect interpretation of the study's results?
Representativeness could be an issue in the findings of the study especially when not applied to
larger population outside the study population. Also this could lead to sampling or selection bias.
Question 9: From this table, calculate the proportion of cases and controls who smoked.
Proportion of cases who smoked: 1350/1357=.99
Proportion of controls who did not smoke: 1296/1357=.96
Cigarette smoker
Cases
Controls
1350
1296
Non-smoker
7
61
Total
1357
1357
1350/1357 =
0.995
0.9550
Proportion Smoked
99.5%
95.5%
Question 10: What do you infer from these proportions?
The proportions for both cases and controls is very close and appear to be same.
Question 11a: Calculate the odds of smoking among the cases.
Odds ratio= [(1,350 * 61) /(1,296 *7)]=82350/9072=9.1
Question 11b: Calculate the odds of smoking among the controls.
Odds ratio of smoking among controls is 99%
Odds ratio of smoking among control =(1,296* 7) /(1,350*61) =0.1 or 99%
Cases
Controls
Cigarette smoker
1350
1296
Non-smoker
7
61
Total
1357
1357
Question 12: Calculate the ratio of these odds. How does this compare with the cross-product
ratio?
Comparing the ratio of these odds is 9.1 and it was compare with the cross ratio by exposure to
smoking which shows that risk of smoking also has effects on other health condition.
Cases
Controls
Cigarette smoker
1350
1296
Non-smoker
7
61
Total
1357
1357
1350/1357 =
0.995
0.9550
Proportion Smoked =
99.5%
95.5%
smokers/non-smokers
192.9
21.2
Odds
192.9/1
21.2/1
(smokers/non-
9.1
smokers)cases]/(smokers/nonsmokers)(controls)
Odds Ratio (OR)
9.1
Question 13: What do you infer from the odds ratio about the relationship between smoking and
lung cancer?
The Odds Ratio (OR) is 9.1, which means smoking increases the risk for lung cancer, and
individuals who smoke are 9 times more likely to develop lung cancer than individuals who do
not smoke.
Question 14: Compute the odds ratio by category of daily cigarette consumption, comparing each
smoking category to nonsmokers.
Daily Number
of Cigarettes
Number of
Cases
Number of
Controls
Odds Ratio
smokers
(cases) *
non-smokers
(controls) A
smokers (controls)
* non-smokers
(cases) B
A/B
0
7
61
-
-
-
-
1-14
565
706
(565*61)/(7*706)= 7.0
34465
4942
7.0
15-24
445
408
(445*61)/(408*7) =9.5
27145
2856
9.5
25+
340
182
(340*61)/182*7)=
16.3
20740
1274
16.3
All smokers
1350
1296
(1350*61)/(1296*7)=
9.1
82350
9072
9.1
The Odds Ratio for 1-14 cigarettes equal to 7.0
The Odds Ratio for 15-24 cigarettes is 9.5
The Odds Ratio for 25+ cigarettes is 16.3
The Odds Ratio for all smokers is 9.1.
Question 15: Interpret these results.
These results can be interpreted as cigarette smoking is a risk factor for lung cancer and that the
odds of developing lung cancer increases with the number of cigarettes a person smokes on daily
basis.
Question 16: What are the other possible explanations for the apparent association?
There could mean there is a correlation between number of cigarette smoked and lung cancer, but that
does not mean smoking cause lung cancer. It could also mean a bias selection, a confounding or error in
information collected.
Question 17: How might the response rate of 68% affect the study's results?
This response rate of 68 percent could suggest there is selection bias in the study.
Question 18: Compute lung cancer mortality rates, rate ratios, and rate differences for each
smoking
category. What do each of these measures mean?
These results can be interpreted the rates of mortality rates increase as the daily number of
cigarettes a person smokes increase.
Daily Number
of Cigarettes
Deaths
Person-years
at Risk
Mortality Rate
per 1,000
person-years
Rate Ratio
Rate
difference per
1000 personyears
0
3
42800
0.07
8.10
0.50
1-14
22
38600
0.57
19.80
1.32
15-24
54
38900
1.39
32.40
2.20
25+
57
25100
2.25
18.60
1.23
smokers
133
102600
1.30
Total
136
145400
0.94
Question 19: What proportion of lung cancer deaths among all smokers can be attributed to
smoking? What is this proportion called?
The proportion of lung cancer deaths among all smokers can be attributed to smoking is 94.6%.
This proportion is called Absolute Risk.
Question 20: If no one had smoked, how many deaths from lung cancer would have been averted?
Based on the proportion rate lung cancer about 95 percent of deaths can be attributed to
smoking. If no one had ever smoked, 133 from lung cancer would have been averted.
Question 21: Which cause of death has a stronger association with smoking? Why?
Lung cancer have a stronger association with smoking. The rate ratio for lung cancer is at 18.5,
whereas the rate ratio for cardiovascular disease is at 1.3. This could mean that there is higher
association between lung cancer and smoking, than it is cardiovascular disease and smoking.
Question 22: Calculate the population attributable risk percent for lung cancer mortality and for
cardiovascular disease mortality. How do they compare? How do they differ from the
attributable risk percent?
Smokers
Non-smokers
ALL
Rate Ratio
Excess
deaths per
1000 personyears
Attributable
risk percent
among
smokers
Lung Cancer
1.3
0.07
0.94
18.5
1.23
95%
Cardiovascul
ar Disease
9.5
7.32
8.87
1.3
2.19
23%
Population attributable risk percent for Lung cancer disease
=(0.94-0.07)/(0.94)*100= 92.5 about 93%
Population attributable risk percent for cardiovascular disease
(8.87-7.32)/8.87*100= 17.4%
Both percentage show death for lung cancer and cardiovascular disease can be attributed to
smoking. However, the population attributable risk percent for lung disease (93%) is much
higher than the population attributable risk percent of cardiovascular disease (17.4%) this could
mean that individual who smoke can have higher risk factor of lung disease and it could be that
there is association between lung cancer and smoking.
Question 23: How many lung cancer deaths per 1,000 persons per year are attributable to smoking
among the entire population? How many cardiovascular disease deaths?
Lung Cancer: 0.87 deaths per 1,000 person-years
Lung Cancer Death =(0.94-0.07)= 0.87
Cardiovascular Disease: 1.54 deaths per 1.000 person-years
Cardiovascular Disease= (8.87-7.32)
Question 24: What do these data imply for the practice of public health and preventive medicine?
The data implies that smokers are at highest risk group for lung cancer compare to the group who
never smoke. Also quitting smoking reduces the risk/mortality rate for lung cancer. Public health
intervention/education such as smoking cessation for individual who smoke will most likely to
reduce mortality rate for lung cancer.
Question 25: Compare the results of the two studies. Comment on the similarities and differences
in the computed measures of association
Both studies show the association between deaths of lung cancer and how is link to smoking.
Both studies also show how the risk factor of cigarettes smoking increased the risk of a lung
cancer. The differences is that rates ratios for the cohort study presents strong evidence then the
odds ratios in the case-control study.
Question 26: What are the advantages and disadvantages of case-control vs. cohort studies?
Advantages/disadvantages
Sample size/cost Study time
Case-control –
Case-control –
Cohort
Cohort
disadvantages
advantages
Disadvantages
Advantages
Smaller size
Cost-effective
expensive
Larger
inexpensive
lengthy- takes
quick results
long time to
conduct it
Rare disease
Not good for rare
Good for
Not good
Good
Rare exposure
exposure
studying rare
looking at
looking at
Multiple exposures
Not good looking
diseases
studying rare
rare
at multiple
Good looking
diseases
exposure
outcomes
at multiple
not good
Good
exposures –
looking at
looking at
multiple
multiple
exposures
outcomes
-
Good
Multiple outcomes
Progression,
Not good looking
-
spectrum of illness
at spectrum of
looking at
Disease rates
illness
spectrum of
Not good looking
illness
at rates of the
Good
disease
looking at
rates of the
disease
Recall bias
Has potential for
-
-
Has
bias
less/minimi
zes recall
bias
Loss to follow-up
Has selection bias
Selection bias
less potential
potential for
Has less
for loss to
loss
selection
follow up
bias
Question 27: Which type of study (cohort or case-control) would you have done first? Why? Why
do a second study? Why do the other type of study?
I would have conducted a case-control study because case control can be used when etiology of
the disease and the information about the disease is available. Case control also is cost effective
and easy to complete, especially for this particular study if we want to know association between
lung cancer and cigarette smoking.
Question 28: Which of the following criteria for causality are met by the evidence presented from
these two studies?
YES
Strong association=
YES
Consistency among studies=
YES
Exposure precedes disease=
YES
Dose-response effect=
Biologic plausibility =
NO
YES
NO
Reference
Friis R.H. and Sellers T. A. (2014) Epidemiology for Public Health Practice, 5th ed.. Jones and
Bartlett