Internal vs External Validity PDF

**INTERNAL VS EXTERNAL VALIDITY** **Internal and external validity are central to understanding the quality and applicability of research findings. Below is a detailed breakdown, including definitions of key terms, examples, and factors that influence each type of validity.** **Internal Validity**...

**INTERNAL VS EXTERNAL VALIDITY** **Internal and external validity are central to understanding the quality and applicability of research findings. Below is a detailed breakdown, including definitions of key terms, examples, and factors that influence each type of validity.** **Internal Validity** **Definition:** **Internal validity refers to the degree to which a study can establish a cause-and-effect relationship between the independent variable (IV) and the dependent variable (DV). It focuses on ruling out alternative explanations for the observed results.** **Key Characteristics:** - **High internal validity means the study successfully isolates the effect of the IV on the DV, with minimal influence from confounding variables.** - **Threats to internal validity reduce confidence that changes in the DV are caused by the IV.** **Key Terms:** - **Confounding Variable: An external factor that influences the DV and is related to the IV, creating an alternative explanation for the results.** - **Experimental Control: Techniques used to eliminate or minimize confounding variables (e.g., random assignment, blinding).** - **Causality: The direct relationship between two variables where one directly affects the other.** **Common Threats to Internal Validity:** 1. **History Effects: External events occurring during the study that affect participants (e.g., news of a global pandemic during a stress-reduction experiment).** 2. **Maturation: Changes in participants over time (e.g., natural development, fatigue).** 3. **Testing Effects: Repeated testing influencing outcomes (e.g., participants improving on a test simply due to practice).** 4. **Instrumentation: Changes in measurement tools or procedures over time (e.g., using a different version of a questionnaire mid-study).** 5. **Selection Bias: Non-equivalent groups due to non-random assignment.** 6. **Attrition: Dropout of participants affecting the comparability of groups.** 7. **Demand Characteristics: Participants altering their behavior based on perceived expectations.** **Examples of Internal Validity in Research:** - **High Internal Validity: A randomized controlled trial (RCT) where participants are randomly assigned to a new drug group or placebo group, and confounders are controlled.** - **Low Internal Validity: A pretest-posttest study on weight loss where some participants join a gym during the study, influencing results independently of the intervention.** **External Validity** **Definition:** **External validity refers to the extent to which the results of a study can be generalized to other populations, settings, times, or conditions.** **Key Characteristics:** - **High external validity ensures that study findings apply beyond the specific sample or context of the study.** - **Threats to external validity limit the applicability of findings to real-world situations.** **Key Terms:** - **Population Validity: The degree to which results can be generalized to the broader population (e.g., studying college students and applying findings to all adults).** - **Ecological Validity: The extent to which the study setting reflects real-world conditions (e.g., testing memory in a quiet lab versus a noisy environment).** - **Temporal Validity: Generalizability of results across time periods (e.g., findings from a study on technology use in 2000 applied to the present day).** **Common Threats to External Validity:** 1. **Sample Characteristics: Results may not generalize if the sample is not representative (e.g., a study on mental health using only college students).** 2. **Setting: Research conducted in highly controlled environments may not reflect real-world settings.** 3. **Time and Context: Findings from past studies may not apply to current social, technological, or cultural conditions.** 4. **Interaction Effects: Effects specific to the interaction between the treatment and sample, limiting generalizability (e.g., a training program effective only for specific age groups).** **Examples of External Validity in Research:** - **High External Validity: A field study on workplace productivity conducted across multiple industries with diverse employees.** - **Low External Validity: A study on anxiety using a small, homogeneous sample of undergraduate psychology students, tested in a lab environment.** **Key Differences Between Internal and External Validity** **Aspect** **Internal Validity** **External Validity** ------------------------------ ----------------------------------------------------------------- -------------------------------------------------------------------- **Focus** **Cause-and-effect relationships** **Generalizability of findings** **Primary Goal** **Minimize confounding variables and alternative explanations** **Apply findings to other populations, settings, or times** **Control vs. Realism** **High control of variables, often at the expense of realism** **High realism, often at the expense of experimental control** **Threats** **History, maturation, selection bias, testing effects** **Sample characteristics, ecological validity, temporal validity** **Example of High Validity** **Randomized controlled trial in a controlled lab setting** **Observational study conducted in naturalistic settings** **Balancing Internal and External Validity** - **Trade-Off: Studies with high internal validity (e.g., tightly controlled lab experiments) often sacrifice external validity because they may not represent real-world conditions. Conversely, studies with high external validity (e.g., field studies) often have lower internal validity due to the lack of control over confounding variables.** - **Maximizing Both:** - **Use random sampling to enhance external validity.** - **Use random assignment and control techniques to improve internal validity.** - **Conduct replication studies across diverse settings and populations.** **Active Recall Questions** 1. **What is internal validity, and how can it be threatened in experimental research?** 2. **Provide an example of high internal validity and low external validity in a psychological experiment.** 3. **Define ecological validity and describe how it relates to external validity.** 4. **How can a researcher improve both internal and external validity in the same study?** 5. **Why might a highly controlled lab experiment lack generalizability?**