Week 4 appendix a article
The threats to internal validity are changes in extraneous variables which can have an impact on the study, such as participant reactivity or bias. The threats to external validity include the possibility of results not being applicable outside of the specific context in which the experiment occurred due to its limited sample size, representativeness, generalizability and other factors.
Additionally, if there is a lack of replicability (due to inadequate procedures that were used) this could also reduce overall validity of findings ultimately either invalidating or undermining credibility any conclusions drawn from it.