Threat	Description	Control
History	Occurrence of events concurrent with the independent variable that could influence/affect the outcome/dependent variable.	a) No extraneous effects that could have changed the ability of the control group to answer the questions of the case scenario took place. b) Both groups were equally compiled. c) No other courses on the subject of critical thinking were offered to the participants before or during the time they were involved in the study. They came directly from rural placement (nursing practice in communities) five weeks prior to the implementation of the educational programme. d) The reminder that was given to the participants kept them in suspense about the content of the educational programme. It only indicated the venue, time and dress code necessary for attending the educational programme.
Selection bias/threat	The composition rather than the treatment of the group may account for the outcome. The threat encompasses biases resulting from pre-existing differences between groups. A selection threat is more likely to occur in studies where randomization is not possible.	a) The inclusion criteria for both the experimental and the control group were the same. b) Participation in the study was voluntary and with written consent. c) The researcher refrained from interfering in the active participation of the participants but merely facilitated the educational programme. d) The inclusion criteria encompassed what the participants had done in their general curriculum at the stage of the programme presentation. Both campuses have participants from different regions, and participants were all in the second semester of their fourth year at the same Department of Nursing, although at different campuses. e) Participants were all at the same level of their education and had done the same curriculum content at the stage of the programme. f) No interference took place at the completion of case scenario questions by the control group. g) By setting criteria for inclusion in the educational programme, similarity between groups had been secured as far as possible. h) Statistical analyses were done to compare groups in order to determine whether the groups were equal in compilation and academic standing before they embarked on the pre-test.
Maturation	Improvements between testing sessions may be the result of routine changes that occur with time. This threat arises from processes occurring as a result of time rather than the independent variable.	a) Participants were at the same developmental stages in their academic achievements since the year of study and other requirements for the completion of their fourth year were similar. b) The post-test was written directly after the educational programme had been completed to limit any external input or influences when the participant went back to practice or lectures. c) The post-test for the experimental and control group was written at the same time.
Instrumentation	Differences may be found because the data collection process has somehow changed. Effects may be due to changes in measurements between the pre-test and post-test rather than a result of the treatment.	a) No changes appeared in the data collection process. b) The pre-test and post-test that were handed to participants in both the experimental and control groups were the same. c) Case scenarios were distributed and collected by the researcher and a research assistant, who had very clear instructions on what to do. d) No changes were made after the reliability of the instrument had been determined.
Statistical regression	Groups selected on the basis of extreme scores tend to shift toward the mean of the original group when retested.	Participants were not drawn from extreme sectors of the population.