WEEK 3: PUTTING A FIGURE AT RISK Flashcards
What is a risk?
The probability/ likelihood of an event to occur.
Event= death, disease, injury or even behavior change
What can be used to estimate risk?
Epidemiology
What is clinical epidemiology?
Science of making predictions about individual patients by counting clinical events in similar patients, using strong scientific methods for studies of groups of patients to ensure that predictions are accurate.
Important approach to obtaining the kind of information clinicians need to make good decisions in the care of their patients.
Outline considerations when using clinical epidemiology.
Patient’s prognosis is expressed as probabilities – estimated by past experience
Individual clinical observations can be subjective and affected by variables that can cause misleading conclusions
Clinicians should rely on observations based on investigations using sound scientific principles, including ways to reduce bias
What is epidemiology?
Process by which public health problems are detected, investigated, and analyzed
Outline the objectives of epidemiology.
To determine the rates of disease by person, place and time
Absolute risk (incidence, prevalence)
To identify the risk factors for the disease
Relative risk (or odds ratio)
To develop approaches for disease prevention
What is incidence?
Number of new cases of a disease occurring in a specified time period divided by the number of individuals at risk of developing the disease during the same time.
What is prevalence?
Total number of affected individuals in a population at a specified time period divided by the number of individuals in the population at the time
Example:
In 2006, 4 new cases of an incurable viral disease were diagnosed in a population with 100 individuals. That brought the total number of affected individuals in the population to 16.
What is the prevalence and incidence of the disease.
The incidence of this disease in this population in 2006 was 4/(100-16). The number at risk was 84 since 16 were already affected.
The prevalence of this disease in this population in 2006 was 16/100.
What is Relative risk /risk ratio (RR)?
RR = ratio of incidence of disease in exposed individuals to the incidence of disease in non-exposed individuals (from a cohort/prospective study)
State the formula for risk ratio/ relative risk.
Formula= Risk among exposed (Re)/ Risk among the unexposed (Ru)
What does a relative risk/ risk ratio less than 1 or more than 1 mean?
If RR > 1, there is a positive association
If RR < 1, there is a negative association
Describe what epidemiologic objectives do the following try to achieve.
*Absolute risk (incidence, prevalence)
*Relative risk (or odds ratio)
*Attributable risk/fraction
To determine the rates of disease by person, place and time
Absolute risk (incidence, prevalence)
To identify the risk factors for the disease
Relative risk (or odds ratio)
To develop approaches for disease prevention
What is odd ratio?
Odds Ratio (OR)= ratio of the odds that cases were exposed to the odds that the controls were exposed (from a case control/retrospective study) – is an estimate of the RR
Formula= Odds among exposed (Oe)/ Odds among the unexposed (Ou)
Odds= p/(1-p)
Interpretation is the similar to RR especially in rare disease conditions
What is attributable risk or fraction?
AR = the amount of disease incidence that can be attributed to a specific exposure
*Difference in incidence of disease between exposed and non-exposed individuals
*Incidence in non-exposed = background risk
.
*Amount of risk that can be prevented
AF = the proportion of disease incidence that can be attributed to a specific exposure (among those who were exposed)
AR divided by incidence in the exposed X 100%
State the formula for AF.
(Risk factor among positive) - (Risk factor among negative)/ (Risk factor among the positive) x 100%
Outline the major epidemiologic study designs.
Case Control (retrospective)
Cohort (prospective)
Cross sectional (one point in time)
Describe what happens in case control studies.
1.Identify affected and unaffected individuals.
2.Risk factor data is collected retrospectively.
Case control or retrospective studies begin by identifying individuals who do and do not have the disease under investigation.
It is important to consider how these individuals are identified to avoid potential selection bias.
Then we determine which individuals were exposed to a particular risk factor by asking them to recall the exposure, going back into medical records where the exposure may have been documented, or using a biomarker to measure the exposure.
These different methods of documenting exposures may not be equally accurate.
State the advantages of case control / retrospective studies.
Advantages
*Inexpensive
*Relatively short
*Good for rare disorders
*Measures of risk
-Odds ratio
-Attributable risk (if incidence is known)
State the disadvantages of case control or retrospective studies.
Disadvantages
*Selection of controls can be difficult
*May have biased assessment of exposure
*Cannot establish cause and effect
Describe what happens in a cohort or prospective study.
Identify unaffected individuals
Risk factor data collected at baseline
Follow until occurrence of disease
State the advantages of a cohort study.
Advantages
Establishes cause and effect
Good when disease is frequent
Unbiased assessment of exposure
Measures of risk
Absolute risk (incidence)
Relative risk
Attributable risk
State the disadvantages of a cohort study.
Disadvantages
Expensive
Large
Requires lengthy follow-up
Criteria/methods may change over time
State the advantages of a cross sectional study.
Advantages
Assessment of disease/risk factors at same time
Measures of risk
Absolute risk (prevalence)
Odds ratio
Attributable risk (if incidence is known)
State the disadvantages of a cross sectional study.
May have biased assessment of exposure
Cannot establish cause and effect
State factors to consider when interpreting study results.
*No such thing as a ‘perfect’ study
*Recognize the limitations and the strengths of any one study
*Critiquing the epidemiology literature:
-Are they comparable in terms of demographic and other characteristics?
-Are they representative of the entire population?
-Are the measurement methods comparable (e.g., eligibility and classification criteria, risk factor assessment)?
-Could associations be biased or confounded by other factors that were not assessed?
