SI- Threats to Internal and External Validity

Internal Validity

Ensures that observed changes in the dependent variable result only from the manipulation of the independent variable.

External Validity

Ensures that research findings can be generalized to other settings, populations, or times.

History (Threat to Internal Validity)

Occurs when uncontrolled events influence outcomes between pretest and posttest.

Maturation (Threat to Internal Validity)

Refers to changes in subjects over time unrelated to the study, such as aging or fatigue.

Attrition (Mortality)

Occurs when participants drop out of a study, potentially skewing results.

Testing (Threat to Internal Validity)

Repeated testing can influence outcomes as subjects learn from previous assessments.

Instrumentation (Threat to Internal Validity)

Changes in measurement tools or data collection techniques can affect outcomes.

Statistical Regression

Occurs when subjects selected for extreme scores naturally move closer to the mean upon retesting.

Selection Bias

Results from non-random assignment, causing systematic differences between groups.

Placebo Effect

When subjects expect improvement, they may report better outcomes even if the treatment is ineffective.

Sample to Population Effect

Occurs when the sample does not adequately represent the target population.

Exposure to Multiple Treatments

Participants may encounter multiple variables, making it hard to isolate individual effects.

Hawthorne Effect

Subjects alter behavior simply because they know they are being studied.

Researcher Effect

The researcher's behavior or characteristics may influence participants.

Pretest Effects

The act of taking a pretest may influence participants’ responses on subsequent assessments.