Chapter 11. - Internal Validity: Threats and Placebo

PSYC 302

Demand Characteristics

Participants alter responses to guess study purpose.

Single-blind Design

Participants unaware of group assignment.

Double-blind Design

Neither participants nor experimenters know group assignments.

Placebo Effect

Improvement due to belief in treatment's efficacy.

Nocebo Effect

Negative outcomes from belief in harmful treatment.

Placebo Control Trial

Study comparing placebo group to active treatment.

Internal Validity Threats

Factors that can compromise study conclusions.

Design Confound

An uncontrolled variable influences results.

Observer Bias

Researcher's expectations affect data collection.

Pre-test/Post-test

Measurements taken before and after treatment.

Maturation

Changes in participants over time affect results.

Attrition

Loss of participants affects study outcomes.

Testing Effects

Participants' performance changes due to repeated testing.

Instrumentation

Changes in measurement tools affect data consistency.

Selection Effects

Differences in groups affect study results.

Order Effects

Participant responses influenced by sequence of conditions.

Null Effects

No significant difference found between groups.

Effect Size

Magnitude of difference between groups.

Ceiling Effect

Scores cluster at high end, limiting measurement.

Floor Effect

Scores cluster at low end, limiting measurement.

Manipulation Checks

Tests to confirm effectiveness of experimental manipulation.

Statistical Power

Likelihood of detecting true effect when present.

Measurement Error

Inaccuracies in data collection affecting results.

Individual Differences

Variability among participants affecting study outcomes.

Situation Noise

External factors that introduce variability in data.

Within-groups Design

Same participants used across all conditions.

Matched Random Assignment

Participants paired based on similar characteristics.

Internal Validity

The extent to which a study accurately establishes cause-effect relationships.

Confounding Variables

Extraneous variables that influence both independent and dependent variables.

Obscuring Variables

Factors that hide or distort the true relationship between variables.

One-group Pretest/Posttest Design

A design measuring participants before and after treatment.

Maturation Threat

Behavior changes due to natural development over time.

History Threat

External events affecting participants simultaneously with treatment.

Regression Threat

Extreme scores tend to move closer to the mean over time.

Attrition Threat

Loss of participants from pretest to posttest affecting results.

Testing Threat

Changes in scores due to repeated testing experiences.

Instrumentation Threat

Changes in measurement tools affecting data consistency.

Observer Bias

Researcher's expectations influence participant behavior or data.

Demand Characteristics

Participants alter behavior to align with study expectations.

Placebo Effect

Improvement due to belief in treatment rather than actual effect.

Nocebo Effect

Negative outcomes due to belief in harmful treatment.

Control Group

A group that does not receive the treatment for comparison.

Double-blind Design

Neither participants nor experimenters know group assignments.

Single-blind Design

Participants are unaware of their group assignment.

Order Effects

Influence of the sequence of conditions on participant responses.

Ceiling Effect

Scores cluster at the high end, limiting variability.

Floor Effect

Scores cluster at the low end, limiting variability.

Power

The likelihood of detecting an effect when there is one.

Weak Manipulations

Insufficiently strong interventions that fail to produce effects.

Error Variance

Unexplained variability in data affecting results.

Individual Differences

Variability among participants that can skew results.