ASSESSMENT OF RISK AND BENEFIT IN EPIDEMIOLOGIC STUDIES Flashcards
- distinction between people who have and people who do not have exposure to the risk factor (or protective factor) under study.
Independent Variable
- distinction between people who have and people who do not have the disease (or other outcome) under study.
Dependent Variable
- difference between the frequency of disease in persons exposed to a risk factor and the frequency of disease in persons not exposed to the same risk factor.
Cohort Studies
, from a defined population, we will not randomly assign a population. We need to know if a certain individual passed the exposure or was not exposed.
cohort study
means a group of people being banded together or treated as a group.
Cohort
focuses on the exposure. We will follow if the exposed people will develop the disease in the outcome.
Cohort
- difference is between the frequency of the risk factor in case participants (persons with the disease) and the frequency of the risk factor in control participants (persons without the disease).
Case-Control Studies
is defined as those who have the disease control those who do not have the disease.
Case-control
start with people who have the disease, then looking back if the sick people were exposed with a certain risk factor.
Case-control
Allow investigators to obtain absolute and relative measures of risk
Cohort studies
Allow investigators to obtain only a relative measure of risk
CASE-CONTROL STUDIES
MEASURES OF RISK FACTORS
- Absolute Risk
- Relative Risk
- Odds Ratio (Relative Odds)
- Attributable Risk
2x2 table
Contingency table
● Incidence of the disease
ABSOLUTE RISK (AbR)
Indicate the magnitude of the risk in a group of people with a certain exposure
ABSOLUTE RISK (AbR)
Only reflects a person’s overall risk of developing the health event
ABSOLUTE RISK (AbR)
DISADVANTAGES
● It does not take into consideration the risk of disease in unexposed individuals
● It does not indicate whether the exposure is associated with an increased risk of the disease
ABSOLUTE RISK (AbR)
Formula of ABSOLUTE RISK (incidence of the disease)
AbR = [a/(a+b)] x 100
What formula to use: What is the absolute risk of lung cancer by smoking status?
AbR = a / (a+b) x 100
Relative risk is also known as the
Risk Ratio (RR)
The ratio of absolute risk (incidence rates) which can be used in cohort studies
RELATIVE RISK (RR)
It determines whether there is an association between exposure to a risk factor and development of a disease
RELATIVE RISK (RR)
Asks the question: How strong is the association?
RELATIVE RISK (RR)
DISADVANTAGES
● Can only be used if your study is a cohort study
RELATIVE RISK (RR)
RELATIVE RISK (RR) Formula
Relative risk = (incidence in exposed / incidence in unexposed)
Formula: Incidence in exposed
a/(a+b)
Formula: Incidence in unexposed
c/(c+d)
ODDS RATIO (RELATIVE ODDS) is also known as
Relative Odds
Can be used in case-control studies and cohort studies
ODDS RATIO (RELATIVE ODDS)
Determines the proportion of cases who were exposed and the proportion of controls who were exposed
ODDS RATIO (RELATIVE ODDS)
FORMULA for ODDS RATIO (RELATIVE ODDS)
Odds Ratio (OR) = Cross Products Ratio = (ad)/(bc)
QUESTION RAISED WOULD BE: Is your exposure a risk factor associated with your development of the disease?
ODDS RATIO: COHORT STUDIES
QUESTION RAISED WOULD BE: Is the exposure associated more with those who have the disease or to those who do not have the disease?
ODDS RATIO: CASE-CONTROL STUDIES
Concordant pairs
EE and NN
Disconcordant pairs
EN and NE
= A way to control the confounding
Matching
• Matching those controls to cases
MATCHED-PAIR CASE-CONTROL STUDY
of cases = # of controls
MATCHED-PAIR CASE-CONTROL STUDY
Helps us control for variables that may confound our results
MATCHED-PAIR CASE-CONTROL STUDY
If we match out cases and controls on a separate variable, then we can see if there is a difference based just on the exposure
MATCHED-PAIR CASE-CONTROL STUDY
Four potential outcomes: of MATCHED-PAIR CASE-CONTROL STUDY
1) Case exposed – control exposed (EE)
2) Case not exposed – control not exposed (NN)
3) Case exposed – control not exposed (EN)
4) Case not exposed – control exposed (NE)
– EE and NN
▪ This means that they are in agreement (i.e., exposed-exposed, not exposed-not exposed
Concordant
– EN and NE
▪ Not in agreement
Disconcordant (or discordant)
In the case of a matched-pair case-control study, when calculating the odds ratio, we are looking at the __________ ONLY
discordant pairs
The _______________ are ignored because they do not contribute to our knowledge of how cases and controls differ in regard to past history of exposure; also, we want to know the difference
concordant pairs (a & b)
CALCULATING ODDS RATIO IF MATCHED-PAIR (Formula)
Odds ratio (matched pairs) = b/c
ratio of the number of pairs that support the hypothesis of an association (pairs in which the case was exposed and the control was not) to the number of pairs that negate the hypothesis of an association (pairs in which the control was exposed and the case was not)
MATCHED PAIR ODDS RATIO
No pairs
Cases and controls are individually counted
UNMATCHED PAIR ODDS RATIO
Unmatched pairs odds ratio: formula
Unmatched pairs odds ratio = ad/bc
- it regards something as being caused by something or someone OR being held responsible for or associated with
Attribute
Measures the proportion of disease in the population (or just in the exposed group) that can be ‘attributed’ to the exposure
Attributable risk
measure how much of the trait would be prevented were it removed from the population
Attributable risk
useful in answering the question of how much disease can be prevented if we have an effective means of eliminating the exposure in question
Attributable risk
How much of the disease that occurs can be attributed to a certain exposure?
Attributable risk
______ and ______ are important measures of the strength of association, which is a critical consideration in deriving a causal inference
Relative risk (RR) and Odds ratio (OR)
is a measure of how much of the disease risk is attributable to a certain exposure
Attributable risk (AR)
is used to evaluate whether the exposure may be a cause of the outcome
Relative risk
is the impact of the cause which leads to the outcome
Attributable risk
is valuable in etiologic studies of disease o Example: help support the case for smoking as a cause of kidney transplant failure
Relative risk
has major applications in clinical practice and public health o Example: describes the impact of smoking on the kidney transplant population
Attributable risk
