Lecture 11 - Problems And Limits Of Epidemiology

Question 1

The ultimate goal of many epidemiological studies is to…..

Answer 1

determine the causes of disease

Question 2

What are the 3 steps in which this “ultimate goal” is accomplished?

Answer 2

1. Observing a possible association between an exposure and an illness
2. Developing a hypothesis about a cause and effect relationship
3. Testing the hypothesis through a formal, epidemiological study

Question 3

While a formal study can strongly support the conclusion that a certain exposure causes a certain disease……

Answer 3

there are many potential sources of error in drawing a conclusion

Question 4

Studies of _______ are especially more prone to error. Why?

Answer 4

chronic diseases because they often have multiple determinants and develop over long periods of time

Question 5

What is the key difference (that poses a potential error) between studying humans and studying animals?

Answer 5

With humans, it is unlikely that participants would remain on the appropriate diet over the necessary length of time - too many temptations

Question 6

it is not realistic to expect to succeed at a randomized, double blind controlled trial that requires people to….

Answer 6

alter their behavior over a significant amount of time (unless if they are suffering from a serious disease and participation is the only way to have access to a new, potentially effective, treatment)

Question 7

instead of a randomized, double blind trial to test a DIETARY hypothesis, what other alternative study could be conducted?

Answer 7

a cohort study - large group of people could be asked detailed questions about their diet and over the next 5 years the health of the 2 groups is compared

Question 8

While a cohort study would NOT require people to change their current behavior, what are some cons associated with this?

Answer 8

people who have voluntarily chosen to eat a healthy diet may differ in other respects than those who eat the average diet (more exercise, less likely to smoke, etc)

CAUSES TOO MANY VARIABLES - HEALTHY LIVING IS THE REASON FOR NO HEART DISEASE - NOT NECESSARILY JUST A HEALTHY DIET

Question 9

What is a 3rd type of study that could be conducted?

Answer 9

case control study

researchers choose a group of heart attack survivors and another group of the same age who HAVENT had a heart attack and question their diets over the past 5 years

Question 10

What are some problems with using a case control study?

Answer 10

-people may forget what they’ve eaten in the past
-Patients might be embarrassed to admit
-Information may not be reliable

Question 11

News reports of new health studies are often confusing and 2 different articles may show contradictory results- what accounts for this?

Answer 11

reported result could be a merely random variation due to chance

Question 12

So that results aren’t contradictory, as a general rule - what is required?

Answer 12

statistical significance
-require a LARGE NUMBER of subjects in studies of chronic disease to draw valid conclusions

Question 13

So that results aren’t contradictory, as a general rule - what is required?

Answer 13

statistical significance
-require a LARGE NUMBER of subjects in studies of chronic disease to draw valid conclusions

Question 14

Why are chronic diseases so difficult to determine the cause?

Answer 14

causes of these diseases are usually complex and there are usually long periods between exposures to potential causes
TOO MANY VARIABLES

Question 15

The weaker the relationship between exposure and disease, the ______ the group of people must be for the relationship to be evident

Answer 15

larger

Question 16

Why were the results concerning smoking and lung cancer (Doll-Hill and Hammond-Horn) so convincing?

Answer 16

they involved a large number of subjects and the link was very strong

Question 17

What are confounding variables?

Answer 17

factors that are associated with the exposure and may independently affect the risk of developing the disease

Question 18

Give an example of a study that may have had some confounding variables?

Answer 18

1980s study that suggested coffee drinking could cause pancreatic cancer

many coffee drinkers are also smokers —> that could have been the cause
THERE HAS BEEN NO INDEPENDENT CONFIRMATION

Question 19

coffee-cancer study —how could these errors be eliminated?

Answer 19

conduct a new study ONLY ON NONSMOKERS

Question 20

Selection bias is a particular problem in choosing subjects for what kind of study?

Answer 20

a case control study (low fat vs high fat diet example. ppl who consume less fat are likely to live a healthier lifestyle in general)

Question 21

Cohort studies extend over many years and are thus likely to suffer from a form of selection bias caused by…..

Answer 21

people dropping out or not responding

Question 22

A ___ drop out rate casts doubts on the result of any epidemiological study

Answer 22

high

Question 23

Reporting bias/recall bias is a problem in what kind of study?

Answer 23

case control study
(ex: birth defects - mother would be reluctant to admit her potential involvement. people who drink heavily tend to under report. underweight individuals may over report their fat intake)

Question 24

What is the most important indication that an epidemiological result is valid? give an example

Answer 24

if the results are consistent with other investigations

ex- british case control study linking birth control to breast cancer only had a 2.3 odds ratio

nurses health cohort study had a 1.5 relative risk

odds ratio is low but it is amplified by the fact that the 2 independent studies yielded the same result

Question 25

Besides different studies having the same result, what is another way to prove a cause and effect relationship?

Answer 25

dose-response relationship -radiologists had the lowest life expectancy of the 3 groups and they're ALSO exposed to radiation the most (highest dose)

Question 26

What is another way that epidemiological evidence is more convincing?

Answer 26

if there is a known biological explanation for association between exposure and disease

Question 27

Most epidemiologic studies are _____ and have little potential for ______. What is the exception?

Answer 27

observational and have little potential for harm exception - intervention studies

Question 28

These days, there are strict ethical limits in any study involving humans. why?

Answer 28

as a result of the abuses of Joseph Mengele who conducted medical experiments on concentration camp prisoners during WW2

Question 29

What are the 3 groups who are most at risk of abuse in medical testing?

Answer 29

-poor patients -prisoners -patients of mental institutions

Question 30

What is the purpose of the Institutional Review Board and why was it founded?

Answer 30

any study to be conducted must be approved by the Institutional Review Board. They must agree that it is: 1. well designed 2. its benefits outweigh its risks 3. Subjects are truly given informed consent Founded because of the syphilis case

Question 31

When does the IRB have the authority to halt a clinical trial?

Answer 31

if the treatment group is clearly showing better or worse results than the control group

Question 32

Give a specific example in which a clinical trial was stopped?

Answer 32

The Physician's Health study - obvious that subjects taking aspirin were suffering fewer heart attacks than those in the placebo group

Question 33

Explain why the AIDS epidemic was different in the case of ethics

Answer 33

people who had AIDS knew that they had a fatal disease and no cure - they were desperate for any access to a new drug even if a clinical trial was not conducted

Question 34

What is the issue when a study is being conducted in which there is already an effective treatment?

Answer 34

people do not want to risk being randomized to the placebo group if they suspect that the already active therapy is effective

Question 35

Give an example TODAY of a study in which there is already an effective treatment?

Answer 35

bone marrow transplants. The National Cancer Institute is sponsoring a trial that requires women to be randomly placed in the transplant group or conventional chemo (current) -many are reluctant to participate because they want the treatment that currently works (NEW TREATMENT HAS 5% CHANCE OF DEATH FROM THE TREATMENT ALONE)