Define internal validity and identify two threats.

Define internal validity and identify two threats.

• A. Internal validity measures the sample size
• B. Internal validity is the extent to which a study demonstrates a causal relationship free from confounds; threats include confounding variables and poor control of extraneous variables or placebo effects
• C. Internal validity is the accuracy of statistical tests
• D. Internal validity concerns external generalizability

Answer: (B)

Internal validity is about whether a study can support a causal claim—that the changes in the independent variable actually caused the observed outcome, rather than other factors. It asks if alternative explanations could account for the results, and aims to rule them out so the relationship appears truly causal. Two common threats to internal validity are confounding variables and poor control of extraneous factors (including placebo effects). A confounding variable varies with the independent variable and can produce the same effect as the treatment, making it hard to tell what caused the outcome. For example, if one group receives more study time in addition to the treatment, the observed improvement might be due to time spent studying rather than the treatment itself. Poor control of extraneous variables means there are other uncontrolled influences that differ between groups, so differences in outcomes could reflect those factors instead of the manipulation. Placebo effects—the idea that participants’ expectations can influence results—can also undermine internal validity by producing changes that are not due to the actual treatment. Strengthening internal validity involves methods like random assignment, using control groups, blinding participants and researchers when possible, and standardizing procedures to keep extraneous influences constant.

Internal validity is about whether a study can support a causal claim—that the changes in the independent variable actually caused the observed outcome, rather than other factors. It asks if alternative explanations could account for the results, and aims to rule them out so the relationship appears truly causal.

Two common threats to internal validity are confounding variables and poor control of extraneous factors (including placebo effects). A confounding variable varies with the independent variable and can produce the same effect as the treatment, making it hard to tell what caused the outcome. For example, if one group receives more study time in addition to the treatment, the observed improvement might be due to time spent studying rather than the treatment itself. Poor control of extraneous variables means there are other uncontrolled influences that differ between groups, so differences in outcomes could reflect those factors instead of the manipulation. Placebo effects—the idea that participants’ expectations can influence results—can also undermine internal validity by producing changes that are not due to the actual treatment.

Strengthening internal validity involves methods like random assignment, using control groups, blinding participants and researchers when possible, and standardizing procedures to keep extraneous influences constant.