External Validity

External validity refers to the extent to which the results of a study can be generalized beyond the specific context of the study to other populations, settings, times, and variables.

Example

Stanford Prison Experiment

The Stanford Prison Experiment is criticized for lacking external validity in its attempt to simulate a real prison environment.

Specifically, the “prison” was merely a setup in the basement of Stanford University’s psychology department.

The student “guards” lacked professional training, and the experiment’s duration was much shorter than real prison sentences.

Furthermore, the participants, who were college students, didn’t reflect the diverse backgrounds typically found in actual prisons in terms of ethnicity, education, and socioeconomic status.

None had prior prison experience, and they were chosen due to their mental stability and low antisocial tendencies.

Additionally, the mock prison lacked spaces for exercise or rehabilitative activities.

Types of external validity

Population validity

Population validity is a key aspect of external validity, which refers to the extent to which research findings can be generalized beyond the specific study context.

Population validity specifically addresses how well the findings of a study can be extended to other populations or groups of people beyond the sample that was studied.

Several factors can impact population validity and need to be carefully considered in research design and interpretation:

• Sampling Methods: The way the sample is selected plays a crucial role in population validity. If the sample is not representative of the target population, the results may not be generalizable.
• For instance, a study using a convenience sample of college students may not accurately reflect the opinions or behaviors of the general adult population.
• Sample Size: The size of the sample also affects the generalizability of the findings. Larger, more diverse samples tend to provide more reliable and generalizable results than smaller, more homogeneous samples.
• Characteristics of the Sample: The specific characteristics of the sample, such as age, gender, ethnicity, socioeconomic status, and cultural background, can influence the generalizability of the findings.

Ecological Validity

Ecological validity concerns the generalizability of findings to real-world settings or environments.

It addresses the question of whether the results obtained in a controlled research context can be meaningfully applied to the natural environments where the phenomenon of interest occurs.

Ecological validity is particularly important in applied research areas like clinical psychology, education, and organizational behavior.

The aim is to ensure that interventions and assessment tools developed in research settings are effective and meaningful in real-world contexts

The superficial resemblance of a study to a real-world situation doesn’t guarantee that the findings will hold true in that context.

For example, using videotaped versus live events in eyewitness memory studies.

The results from a study using live events might be more ecologically valid for real-world scenarios involving live events, while studies with videotaped events could be more relevant for situations like a security guard’s memory of events observed on security monitors.

Researchers should articulate the assumptions about similarities and differences between the two contexts to justify the application of research findings.

The basis for judging the applicability of research findings to real-life setting include the overlap between the cognitive, emotional, and physical aspects of the study and the real-world case.

Threats to ecological validity can arise from the artificiality of the research setting or interactions between the intervention and the context.

Threats to Ecological Validity

1. Artificiality of the Research Setting

• Laboratory Environments: Research conducted in controlled laboratory settings often prioritizes internal validity (controlling extraneous variables) over ecological validity. This can create artificial conditions that do not reflect the complexities and nuances of real-world environments.
  • For example, studying human behavior in a sterile laboratory may not accurately capture how people behave in their natural social settings.
• Participant Reactivity: When people are aware that they are being observed, they may alter their behavior, leading to responses that are not representative of their typical actions in real-life situations. This phenomenon, known as participant reactivity or the Hawthorne effect, poses a significant threat to ecological validity.
• Simplified Tasks and Stimuli: Researchers often use simplified tasks and stimuli in laboratory settings to isolate specific variables and control for confounding factors. However, this simplification can reduce the ecological validity of the findings.
  • For instance, using word lists to study memory may not accurately reflect how people remember information in their daily lives, where memories are often embedded in rich contexts and associated with emotions and experiences.

2. Lack of Attention to Contextual Factors

• Ignoring Environmental Influences: Ecological validity is compromised when research designs fail to account for the impact of environmental factors on the phenomenon being studied.
  • For example, a study on work performance conducted in a quiet, climate-controlled office may not accurately reflect the challenges of working in a noisy, open-plan environment.
• Overlooking Cultural Differences: Cultural norms, values, and beliefs can significantly influence behavior. Studies that do not consider cultural variations may produce findings that are not generalizable across different cultures.
• Neglecting the Dynamic Nature of Behavior: Human behavior is dynamic and changes over time and in response to various internal and external factors. Static research designs that do not capture this dynamism may lack ecological validity.
  • For example, a one-time assessment of employee satisfaction may not provide a complete picture of how satisfaction fluctuates over time in response to workplace changes, job demands, and personal circumstances.

3. Mismatch Between Research Goals and Application Contexts

• Testing Abstract Constructs vs. Real-World Problems: Research often focuses on testing abstract theoretical constructs, which may not directly correspond to the specific problems or challenges faced in real-world settings.
  • For example, a study investigating the cognitive processes involved in decision-making may not provide clear guidance on how to improve decision-making in complex, real-life situations where emotional factors and social pressures also play a role.
• Emphasis on Internal Validity at the Expense of External Validity: The rigorous control of variables required for internal validity can sometimes create conditions that are so artificial that the findings have limited ecological validity.
  • While it is crucial to establish a causal relationship between variables, researchers should strive to achieve a balance between internal and external validity to enhance the applicability of their work.
• Lack of Relevance to Stakeholders: Research that is not perceived as relevant or useful by stakeholders, such as practitioners, policymakers, or community members, is less likely to be implemented in real-world settings, regardless of its ecological validity.
  • Researchers should engage with stakeholders throughout the research process to ensure that the questions being addressed, the methods being employed, and the findings being generated align with the needs and priorities of those who will ultimately use the research results.

4. Failure to Consider Social and Ethical Implications

• Ignoring Potential Negative Consequences: Research findings should extend beyond statistical considerations to encompass the social and ethical implications of test use and the application of research results. Failing to address these potential consequences can undermine the ecological validity of research by overlooking the real-world impact of the work.
• Lack of Attention to Value Judgments: Research is inherently influenced by value judgments, both in the selection of research questions and in the interpretation of findings. Ignoring these value judgments can lead to a skewed understanding of the phenomenon being studied and limit the ecological validity of the research.

Threats to Population Validity

1. Sampling Issues

• Samples Bias: Using samples that are not representative of the target population can severely limit the generalizability of the findings.
  • If a study on the effectiveness of a new therapy only recruits participants who are highly motivated and have good access to transportation, the results may not generalize to a broader population that includes individuals with lower motivation or limited access to care.
  • A study on the effectiveness of a weight loss program might have selection bias if participants are primarily highly motivated individuals with strong social support systems
• Homogeneous Samples: Studies with homogeneous samples, lacking diversity in terms of age, gender, ethnicity, socioeconomic status, and other relevant characteristics, face challenges in generalizing the findings to more heterogeneous populations.

2. Attrition

Attrition is also known as participant dropout, attrition, particularly when differential across groups, can threaten both internal and external validity.

When certain types of individuals are more likely to drop out of a study, the remaining sample may no longer be representative of the original population, making it difficult to generalize the findings.

For example, in a study on the effectiveness of a demanding therapy program, less motivated individuals might drop out at a higher rate, leading to an overestimation of the program’s effectiveness for the general population.

3. Interaction Effects of Selection

Even when selection and mortality are controlled for internal validity, these factors can still impact representativeness.

The obtained effects might be specific to the particular experimental population and not hold true for other groups.

For example, an educational intervention that works well for students in a suburban school might not be effective for students in an under-resourced urban school due to differences in the student populations and learning environments.

How can external validity be improved?

Researchers can employ several strategies to improve external validity:

• Use a representative sample: Recruit participants who are similar to the population of interest in terms of relevant characteristics. Probability sampling techniques, such as random sampling or stratified random sampling, can help ensure that the sample is representative.
• Using Large and Diverse Samples: Larger samples with a wide range of characteristics are more likely to represent the target population and reduce sampling error.
• Carefully Consider Inclusion/Exclusion Criteria: Ensure that these criteria do not inadvertently introduce bias or exclude significant segments of the target population
• Conduct the study in a naturalistic setting: Whenever possible, conduct the study in a setting that is similar to the real-world environment where the findings are intended to be applied.
• Minimize Attrition: Engage strategies to retain participants, such as providing incentives, maintaining regular contact, and making study participation as convenient as possible
• Replicate the study with different samples and settings: Repeating the study with different participants and in different settings can provide evidence for the generalizability of the findings.
• Use multiple measures: Measure the variables of interest in multiple ways to reduce the influence of measurement error and method variance.

How is external validity related to internal validity?

The relationship between internal and external validity can be understood in terms of the interplay between sampling and causal inference.

Internal validity focuses on the accuracy of causal inferences within the sample, while external validity concerns the generalizability of those inferences to the population of interest.

While both are important, internal validity is generally considered a prerequisite for external validity.

If a study lacks internal validity, meaning that there are alternative explanations for the results other than the intended manipulation, then the findings cannot be confidently generalized to other situations.

It’s important to acknowledge that maximizing external validity is not always feasible or necessary.

Some studies are intentionally designed to test specific hypotheses in highly controlled laboratory settings.

These studies might not be intended to be directly generalizable to real-world situations. However, even studies with limited external validity can be valuable for advancing theoretical understanding and informing future research that can explore generalizability.

How does external validity apply to qualitative research?

While the concept of external validity originates from quantitative research, it has relevance for qualitative studies as well.

In qualitative research, the focus often shifts from statistical generalizability to the transferability of findings.

Transferability refers to the extent to which the insights and themes generated from a qualitative study can be applied to other contexts or populations.

Qualitative researchers can enhance transferability by:

• Providing rich, detailed descriptions of the study context, participants, and data collection methods. This allows readers to assess the potential relevance of the findings to their own situations.
• Involving participants in reviewing and validating the findings. This can help ensure that the interpretations resonate with the lived experiences of the participants.
• Explicitly discussing the limitations of the study and the potential boundaries of transferability.
• Focusing on theoretical generalizability rather than statistical generalizability. This involves developing theoretical explanations that can be applied to other contexts, even if the specific findings are not directly replicable.