EPIB Exam 2

Ecological study

Examine the occurrence of disease and other factors in a population using existing statistics that are measured at the group level.

Advantages of ecological studies

Low cost, useful to examine rates of disease in relation to a population level factor

Disadvantages of ecological studies

Ecological fallacy (things that are true of a group are not always true of the individual), cannot make inferences about individuals with group level data

Ecological fallacy

Misleading conclusion about the relationship between factor and an outcome

Ecological fallacy example

Basketball is a popular sport at UMD therefore if you go to UMD, you must like basketball

Cross sectional study

Group of people is observed or certain information is collected at a single point in time or over a short period of time

Advantages to cross sectional study

Ability to use a large representative population (increases generalizability), low cost, less time consuming

Disadvantages to cross sectional study

Cannot infer temporal sequence, cannot be used to meet Hill’s temporality criterium

Case control study remember

Always retrospective

Case control study

Compares individuals who have a specific disease/outcome with those who do not to determine the relationship betwwen a risk factor and that outcome

Advantages to Case control study

Efficient to rare diseases, efficient for diseases that take a long time to develop, can evaulate many risk factors (exposure) for the same disease

Disadvantages to Case control study

Can only consider a single outcome per study, may have poor information on exposure because of retrospective data collection (like recall bias)

Cohort studies remember

Prospective and retrospective

Cohort studies

Observational research design that follows a group of people sharing common characteristics over time to determine how initial exposure affect health outcomes

Prospective cohort study

measure association between an exposure and risk of disease in the population moving forward in time

Advantages of prospective cohort study

collection on lots of exposures and outcomes and ability to establish a temporal sequence

Disadvantages of prospective cohort study

Expensive, time-consuming, and inefficient for disease that take a long time to develop

Retrospective cohort study

measure association between an exposure and risk of disease in the population moving backward in time

Retrospective cohort advantages

Efficient for diseases with long latency periods, temporal sequence only when good historial records are used, relative low-cost, quick to accomplish ONLY when historical records are used

Retrospective cohort disadvantages

May have poor information on exposure and other key variables, recall bias

Randomization

Each study participant has the same probability of being assigned to the treatment group

Compliance

Following the study protocl exactly as required through the course of the trial

Matching

Selecting pairs of clusters of individuals who are comparable on important variables

Randomized controlled trial

Investigator randomizes participants to a treatment of control condition to generate evidence for a causal relationship between an exposure and disease

Randomized controlled trial advantages

“gold standard” of study, high internal validity, temporality sequence is clear, feasible and ethical, treatment and outcome status is clear

Randomized controlled trial disadvantages

lack of generalizability/external validity, experimental setting (doesnt resemble real world), expensive, logistically challenging

Quasi experimental study

Like an experiment but lacks random assignment to treatment and control groups; investigator manipulates the study factor (exposure) but does not assign individuals to treatment groups

Quasi experimental study advantages

Retains some experimental methods when individual randomization may not be feasible, can be used to study a group-level exposure

Quasi experimental study disadvantages

Lacks randomization, participants characteristics are often not balanced at baseline, could be contamination of study groups

Odds ratio remember

Always the association for case-control studies

Odds ratio

A measure how strongly an event is associated with exposure

Selection bias

Healthy worker effect, survivor bias, self selection bias, non-response bias, loss to follow up bias

information bias

hawthorne effect/surveillance bias, revall bias, interviewer bias, measurement error, reporting bias

Confounding variable

third variable that affects the relationship between the exposure and health outcome

Temporality

Exposure must be before the disease/outcome; only criterium that MUST be met

Strength of association

Measures the magnitude of the relationship between an exposure and an outcome, indicating how likely a casual link exists

Biological gradient/ dose response relationship

As exposure to the risk factor increases, risk if disease/outcome either increases or decreases

Specificity of Association

Exposure consistently leads to a single outcome (little to no alternative explanations for the relationship)

Experiment Al evidence

Exposure and outcome have been associated through well-controlled randomized trials

Consistency

Relationships demonstrated in multiple studies across different populations, study designs, and circumstances are more likely to be casual

Plausibility

A mechanism exists that connects the exposure to the outcome

Coherence

Proposed association must not contradict current scientific knowledge

Analogy

Proposed association mirrors another association already established in the literature

Deterministic

A cause is invariably followed by an effect

Probabilistic

Incorporates elements of randomness

Necessary cause

A factor/event that must occur for the specific disease to occue

Sufficient cause

A set of factors that, when come together, inevitably produces a specific health outcome

Casual inference

process of determining whether an association between an exposure and an outcome is truly caused by that exposure rather than bias or confounding

Counterfactual

the condition that is counter to the factual condition

Internal validity

the degree to which a study's results represent the true relationship between exposure and outcome for the participants studied, free from systematic errors

External validity

Generability: the extent to which study results apply to populations, settings, or times beyond the study sample

Random error

Even if the study is done correctly, the observed associaiton could be incorrect

Under Observation umbrella

Cohort, Case-control, Cross sectional

Under experiment umbrella

Randomized control trial (RCT), Quasi experiment

RR>1

Positive association (increased risk)

RR<1

Negative association (decreased risk)

RR=0

No association (null hypothesis)