External and Internal Validity

Summary

This script discusses the importance of validity in research, focusing on internal and external validity. External validity ensures findings can be generalized to other populations and settings, while internal validity confirms the accuracy of measures within the study. The script outlines common threats to both, such as participant characteristics, setting, timing, selection bias, sample size, and confounding variables, emphasizing the need for careful study design to ensure reliable and generalizable results.

Takeaways

• 🔍 Research validity is about the soundness of the research design and methods.
• 🌐 External validity is the ability to generalize study findings to other populations and settings.
• 🚫 Lack of external validity means findings are limited and may not apply to other people or contexts.
• 🔬 Internal validity concerns the accuracy of measures within the study and the true relationship between variables.
• 🚫 Lack of internal validity suggests that findings may not reflect the intended constructs or relationships.
• 👥 Participant characteristics can affect external validity if they do not represent the larger population.
• 🏫 The controlled research environment can limit external validity due to its artificiality compared to real-world settings.
• ⏳ Timing is crucial; past studies may not have external validity in the present due to societal changes.
• 🎯 Selection bias can affect both external and internal validity if groups are not comparable at the study's start.
• 🔢 Small sample sizes can lead to unreliable statistics and findings that may be due to chance.
• 🔄 Confounding variables can undermine internal validity if they influence the dependent variable alongside the independent variable.
• 📚 History effects, such as external events, can impact how participants respond and affect internal validity.
• 📈 Maturation effects, like aging or fatigue, can internally influence responses over the course of a study.
• 🛠️ Instrumentation issues arise when measurement tools change, potentially skewing study results.
• 📝 Testing effects can occur in pre- and post-tests, where familiarity with the test can improve performance.
• 🔄 Attrition refers to participants leaving a study, which can introduce bias and affect both internal and external validity.

Q & A

What does 'validity' mean in the context of research design and methods?

In research, 'validity' refers to the soundness of the research design and methods used to ensure that the findings are accurate and meaningful.

What are the two main types of validity discussed in the script?

The two main types of validity discussed are internal validity and external validity.

Why is external validity important in research?

External validity is important because it allows researchers to generalize their findings to other populations and settings, extending the applicability of the research beyond the specific study context.

What does a lack of external validity imply about the research findings?

A lack of external validity implies that the research findings cannot be confidently applied to other people or contexts outside of the study, limiting the scope of the research's applicability.

What is internal validity and why is it crucial for a study?

Internal validity relates to the accuracy of the measures within a study and ensures that the findings reflect the true relationship between the independent and dependent variables, without being influenced by extraneous factors.

What are some common threats to external validity?

Common threats to external validity include participant characteristics, the research environment, and timing, all of which can reduce the generalizability of the study results to other populations and settings.

How can the research environment affect external validity?

The research environment, often being highly controlled and artificial, may not represent the real-world contexts to which researchers wish to generalize their findings, thus affecting external validity.

What are some threats to internal validity that can compromise a study's findings?

Threats to internal validity include selection bias, sample size, confounding variables, history, maturation, instrumentation, testing or practice effects, and attrition or mortality.

Why is controlling extraneous variables important for internal validity?

Controlling extraneous variables is important for internal validity because it ensures that any changes in the dependent variable are due to the independent variable, not other factors, thus establishing a clear causal relationship.

How can sample size impact the internal validity of a study?

A small sample size can reduce internal validity because it may lack the statistical power needed to produce reliable results, making the findings more susceptible to being due to chance.

What is meant by 'selection bias' and how can it affect both internal and external validity?

Selection bias occurs when the groups being compared in a study are not similar at the outset, potentially due to differences in participant characteristics. This can affect both internal validity by influencing the study's results and external validity by impacting the generalizability of those results.

Can you explain the difference between 'history' and 'maturation' as threats to internal validity?

History refers to external events that occur during the study that may affect participant responses, while maturation is an internal process, such as aging or fatigue, that naturally occurs and can influence the results. Both can affect how participants respond, but history is external, and maturation is internal.

What is 'instrumentation' and how can it threaten the internal validity of a study?

Instrumentation occurs when the measurement tool or method used in a study changes over time, potentially producing different results. This can threaten internal validity by introducing variability in the data collection process that is unrelated to the study's variables of interest.

How can 'testing' or 'practice effects' impact the internal validity of a study?

Testing or practice effects occur when participants perform better on a test the second time due to familiarity or practice, which can lead to improved performance not related to the study's independent variable, thus threatening internal validity.

What is 'attrition' and how can it affect both internal and external validity?

Attrition refers to participants dropping out of a study. It affects internal validity by potentially introducing bias if the reasons for dropping out are related to the study's variables. It can also affect external validity if the group that remains in the study differs significantly from the general population.