Quantitative study: https://pubmed.ncbi.nlm.nih.gov/21986350/

Qualitative Study: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5813303/pdf/14.pdf

review both the methods and the limitations stated by the authors to identify where there may be plausible threats to internal validity. The test of plausibility is more than just being possible. There needs to be some real expectation of likelihood. For quantitative research, the possible threats to Internal Validity in a study include:

• history,
• maturation,
• testing,
• instrumentation,
• subject selection, and
• subject attrition/mortality.

For qualitative research, the possible threats to Internal Reliability in a study include:

• low-inference descriptions
• multiple researchers
• participant researchers
• peer examination
• mechanically recorded data