What is the Difference Between Internal and External Validity?

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The difference between internal and external validity lies in their focus and application in research studies. Here are the key distinctions between the two:

  • Internal Validity:
  • Refers to the degree of confidence that the causal relationship being tested is not influenced by other factors or variables.
  • Examines whether the study design, conduct, and analysis answer the research questions without bias.
  • Focuses on the experimental design and methods of the study.
  • Considers threats to internal validity, such as history, maturation, instrumentation, testing, selection bias, regression to the mean, social interaction, and attrition.
  • External Validity:
  • Refers to the extent to which the results of a study can be generalized to other contexts.
  • Examines whether the study findings can be applied to other situations or populations.
  • Focuses on the generalizability of the study's findings.
  • Includes two types of external validity: population validity (whether the results can be generalized to other populations) and ecological validity (whether the results can be generalized to other situations or environments).

There is often a trade-off between internal and external validity. Better internal validity may come at the expense of external validity, and vice versa. For example, experimental conditions that produce higher degrees of internal validity (e.g., artificial labs) tend to be highly unlikely to match real-world conditions, making external validity weaker. On the other hand, to produce higher degrees of external validity, experimental conditions should match a real-world setting, which may compromise internal validity.

Comparative Table: Internal vs External Validity

Internal and external validity are concepts that reflect whether the results of a research study are trustworthy and meaningful. Here is a table comparing the differences between internal and external validity:

Internal Validity External Validity
Concerned with control of extraneous variables Focuses on the generalization of results to other settings and situations
Determines the accuracy of the experiment Assesses the applicability or generalizability of the findings to the real world
Measures the strength of the causal relationship between the independent and dependent variables Examines whether differences between samples or populations can be attributed to the independent variable
Relies heavily on experiments in which researchers manipulate variables Relies heavily on naturalistic observation
High internal validity often comes at the expense of external validity, and vice versa High external validity often comes at the expense of internal validity, and vice versa

In summary, internal validity ensures that the results of a study are true within the context of the study, while external validity ensures that the results can be applied to other contexts and situations. There is often a trade-off between internal and external validity, as high internal validity can lead to lower external validity, and vice versa.