How can you increase external validity in experimental research without compromising internal validity?

1 Why validity matters

Validity is the quality of an experiment that determines how trustworthy and meaningful its results are. Without validity, an experiment cannot provide reliable evidence or insights for a research question or problem. Validity can be affected by many factors, such as the design of the experiment, the selection of participants, the methods of data collection and analysis, and the interpretation of the findings.

2 Internal validity

Internal validity is the degree to which an experiment can establish a causal relationship between the independent variable (the factor that is manipulated) and the dependent variable (the outcome that is measured). Internal validity depends on controlling or eliminating any confounding variables (factors that can influence the outcome but are not part of the experiment) and minimizing any sources of bias or error. For example, if you want to test the effect of a new teaching method on students' learning outcomes, you need to ensure that the students in the experimental and control groups are comparable, that the only difference between them is the teaching method, and that the assessment of their learning outcomes is fair and accurate.

3 External validity

External validity is the degree to which the results of an experiment can be generalized or applied to other contexts, populations, or situations. External validity depends on the representativeness and relevance of the sample, the setting, and the procedures of the experiment. For example, if you want to test the effect of a new teaching method on students' learning outcomes, you need to consider whether the students in your experiment are representative of the students you want to target, whether the classroom environment is similar to other classrooms, and whether the teaching method is feasible and appropriate for other teachers and subjects.

4 The trade-off between internal and external validity

There is often a trade-off between internal and external validity, meaning that increasing one may decrease the other. This is because internal validity requires a high level of control and standardization, which may limit the variability and diversity of the experimental conditions and participants. On the other hand, external validity requires a high level of realism and flexibility, which may introduce more confounding variables and sources of noise. For example, if you want to test the effect of a new teaching method on students' learning outcomes, you may have to choose between using a random sample of students from different schools and backgrounds, which may increase external validity but decrease internal validity, or using a homogeneous sample of students from the same school and class, which may increase internal validity but decrease external validity.

5 How to increase external validity without compromising internal validity

No single answer exists for how to increase external validity without compromising internal validity, as it depends on the research question, design, and context of the experiment. To achieve this goal, one could use multiple methods of data collection and analysis, such as interviews, observations, surveys, tests, and documents. This approach would add depth and richness to the data, as well as triangulate and validate the findings. Moreover, multiple cases or sites for the experiment may be used to compare and contrast the results across various settings and situations. Additionally, purposive or stratified sampling techniques can be utilized to ensure that the sample reflects the population of interest. Finally, participatory or collaborative approaches involving participants or stakeholders in the design, implementation, or evaluation of the experiment can increase the realism and authenticity of the data.

6 Why this is important for qualitative research

Qualitative research is a type of research that focuses on exploring and understanding the meanings, experiences, and views of people in relation to a phenomenon or problem. Qualitative research often uses experimental methods, such as case studies, action research, or ethnography, to generate rich and detailed data that can provide insights and explanations for complex and dynamic situations. Qualitative research values the diversity and complexity of human phenomena, and aims to produce findings that are relevant and useful for practice and policy. Therefore, increasing external validity without compromising internal validity is important for qualitative research, as it can enhance the quality, rigor, and value of the research.