3.4 types of validity
- 1. 1 Types of validity • Overall definition of validity: A study design and analysis plan are valid if, on average (aside from random error), results generated from the study design reflect the true causal effect in the source population* • A faulty study design and/or analysis plan will, on average, produce biased results...meaning that results will not reflect the true causal effect in the source population*
- 2. Populations and types of validity Study population (sample) Actual Population Target Population External Population Statistical inference Internal validity External validity JC: “Sample” JC: ”Available” JC: “RQ” JC: “Generalizable” 33 Adapted from Kleinbaum, Kupper and Morgenstern, 1982
- 3. 3 Types of validity • There are two types of validity depending on the source population of interest – Internal validity – External validity • Can understand these types of validity in the context of the hierarchy of populations
- 4. 4 Types of validity • * Type of validity depends on the source population of interest for generalization • Internal validity: – The extent to which findings from the study population reflect the true underlying parameters/causal effect in the target population • External validity: – The extent to which findings from the study population reflect the true underlying parameters/causal effect in a defined external population beyond the target population
- 5. Populations and types of validity Study population (sample) Actual Population Target Population External Population Statistical inference Internal validity External validity JC: “Sample” JC: ”Available” JC: “RQ” JC: “Generalizable” 36 Adapted from Kleinbaum, Kupper and Morgenstern, 1982
- 6. 6 Types of validity • Internal validity is a pre-requisite for external validity, and is the primary concern • A study may lack external validity, but even if we can’t generalize results to some external population, the findings are still meaningful if the study is internally valid • If a study lacks internal validity then it necessarily lacks external validity as well • As such, lack of internal validity is the primary concern