Two key concepts in relation to experimental and quasi-experimental design  are internal and external validity.

Internal validity refers to the extent to which a study can establish a cause-and-effect relationship between the intervention and the observed outcomes, ensuring the results are attributable to a particular variable and not influenced by other factors or variable. For example, to what extent an  activity leads to a particular social change.    This can be more challenging in quasi-experimental design due to the lack of random assignment, although  this can be

• Matching: Ensuring that the treatment and comparison groups are similar on key characteristics.

• Using control variables: Accounting for potential confounders in the analysis.

• Pre-tests and post-tests: Measuring outcomes before and after the intervention to observe changes attributable to the intervention.

• Difference-in-differences analysis: Comparing changes in outcomes over time between the treatment and control groups.

• External validity refers to the extent to which the findings of a study can be generalized to other settings, populations, and times.

Internal validity	External validity
The degree to which your impact evaluation establishes a causal relationship between variables, ensuring that the results are attributable to the particular r variable rather than other factors.    The CleanAir Foundation used a Randomized Controlled Trial (RCT) to  assess the impact of their Anti-Pollution Education Campaign. Schools were randomly assigned  to either participate in the campaign or serve a s a control group. The study controlled for potential confounding factors such as school size, location, and existing environmental education programmes. Data on students’ knowledge and attitudes towards pollution were collected through h pre- and post-intervention surveys administered by researchers who were blinded to group assignments, ensuring that changes could be directly linked to the campaign.	The extent to which the results of a study can be generalized beyond the specific conditions of the activities to other populations, settings, times, and measures.    To ensure generalizability, the CleanAir Foundation selected a diverse sample of schools from urban, suburban, and rural areas, representing a wide range of socio-economic backgrounds. The educational materials and activities were designed to be easily adaptable to different contexts, reflecting realistic implementation conditions. The evaluation spanned an entire academic year, capturing seasonal variations in pollution awareness and behaviour, thereby enhancing the applicability of the findings to other settings interested in implementing similar anti-pollution education initiatives.

Sources:

American Psychological Association (APA)

Encyclopaedia Britannica

Internal vs. External Validity | Understanding Differences & Threats (scribbr.com)