The Core Problem
A frequent pitfall is **confounding**, where an unobserved factor links two observed ones, leading to a false correlation.
The Gold Standard: RCTs
Randomization reigns supreme. By creating equivalent groups, it severs ties to hidden biases. This allows any outcome difference to be directly linked to the intervention.
Population
Treatment Group
Control Group
Difference-in-Differences
Evaluates outcome shifts over time, contrasting treated and untreated groups. Requires the "parallel trends" assumption.
Regression Discontinuity
This method analyzes outcomes near a defined threshold, comparing those just on either side, assuming close similarity.
More Tools
Instrumental Variables (IV)
Employs an "instrument" variable impacting treatment selection, yet not the outcome itself, to create a quasi-random assignment.
Propensity Score Matching (PSM)
Here are a few options, all similar in length: * Builds a control group by matching untreated individuals to treated ones with similar treatment propensities. * Forms a control group by finding untreated individuals similar to treated ones based on treatment likelihood. * Generates a control group by pairing untreated individuals with treated individuals, considering their propensity scores. * Creates a matched control group: untreated individuals are paired with treated individuals with a similar treatment chance.
The Unspoken Rules
Analyzing cause from non-experiments hinges on unproven assumptions. These require validation via expert understanding.
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SUTVA
Here are a few options, all similar in length: * Units are independent, treatment is transparent. * Units unaffected, treatment fully visible. * No unit interaction, treatment is explicit. * Independent subjects, clear treatment delivery.
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Unconfoundedness
* All confounding variables are accounted for. * Confounders have been identified and addressed. * We've controlled for all relevant variables. * The analysis considers all key influences. * Potential biases are adequately managed.
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Positivity
Everyone, regardless of their characteristics, has a chance of being assigned to either group.