Validity Issues

Internal validity can be threatened by: ​

• Bias (bias in collection, statistical analysis or interpretation) ​

• Random Error

External Validity can be threatened by: ​

• External validity is dependent on internal validity. Therefore, it is important to address any issues of internal validity in the study design. ​

• Insufficient external validity may make the study results less relevant for application in clinical practice or in the general population.​

• Applicability issues: even if effectiveness is established, this may not always mean it is widely applicable.

(Spieth et al., 2016)