Module 6 Flashcards
Cumulative Incidence Ratio
cumulative incidence in exposed/cumulative incidence in unexposed
The ratio of the risk of disease in exposed individuals to the risk of disease in unexposed individuals. This is a measure of relative risk
Incidence Rate Ratio
Incidence rate in exposed/incidence rate in unexposed
The ratio of the rate of disease in exposed individuals to the rate of disease in unexposed individuals
Odds Ratio
(a/b)/(c/d) = ad/bc
In a case-control study, the odds ratio is calculated as the measure of association because risk cannot be estimated in these study designs
Attributable Risk
The amount or proportion of disease incidence that can be attributed to a specific exposure
Whereas relative risk is important in establishing etiological relationships, the attributable risk addresses “how much of the risk of disease can be hope to prevent if we are able to eliminate exposure to the agent in question”
What is a study?
A scientific process of answering a question using data from a population
Ecological Study
Measurements are made on a group of people. Results apply to a group, not an individuals. Good for comparing rates across populations. Good for developing questions for further investigation and for comparing rates of disease across groups
Case Series
Describes a group of characteristics from a group of people with the same disease or same exposure. Understand the demographics, presentation, prognosis or something unusual.
Cross sectional
Gathers health information at a point in time. Usually a questionnaire. Also called prevalence study. Important to make sure that the study population is representative of the overall population. Relatively inexpensive and good ad assessing exposure/outcomes, and health needs. Cannot be used to determine if a disease is attributable to a specific exposure (no causality). Can be called prevalence studies
Case Control Study
Starts with cases (people with a disease) and compares against controls. Past history is collected and risks are analyze across cases and control. Odds ratio. >1 - associated with the disease; <1 protective factor; 1 = no association
Commonly used in food born outbreak.
Quick and cheap. Good for uncommon diseases. Small numbers and not good for rare exposures. Recall may impact. Challenge to find matched controls
Cohort
Group is followed over a period of time along with risk factors; Can look at occur ace based on risk factors. These studies start with exposures. Individuals with and without exposure to a variable of interest are followed to see if they develop over time. There should be no cases of the disease at the start of the cohort study
Relative risk is the main measure. >1 - increased risk; 1 = same; <1 - lower risk
Time sequence of events can be determined. Can find causes of a disease. Can also collect additional risk factors leading to sub analysis
High cost
Not suitable for rare diseases
Have to account for attrition
Interventional Study
Intervention is done and outcome is studies (e.g., vaccine, education); Randomized control study is the best interventional study design. Double blind is best.
Main advantage - good evidence that an intervention led to an outcome; randomization supports causality
Disadvantage is that they are expensive; many participants; not always possible
Summaries
Systematic review - analysis of all relevant studies
Meta analysis - studies of similar design; uses data to come up with a combined statistical analysis
Relative measures
Help us understand the strength of association between exposure and a disease - helps us understand the etiology of the disease
Absolute measures
Help us understand how much of the disease can be prevented if we have an effective way to eliminate the exposure. THESE MEASURE ASSUME A CAUSAL RELATIONSHIP
What is a necessary and sufficient cause
A factor that is both necessary and sufficient for producing a disease. Without that factor, the disease never develops, and in the presence of that factor, disease always develops. A one-to-one relationship of exposure to disease rarely, if ever, occurs
What is a necessary but not sufficient cause
When each factor is necessary but not in itself sufficient to cause a disease. Thus, multiple factors are required, often in a temporal sequence. H. pylori is an example
Sufficient but not necessary cause
When the factor alone can produce the disease but so can other factors acting alone. Because many exposures may cause disease in some individuals but not others, factor are rarely sufficient but not necessary
Neither sufficient or necessary
When a factor is neither sufficient or necessary to produce disease. Neither sufficient nor necessary cause models probably most accurately represent the causal relationship for most chronic conditions.
