A 4-week randomized clinical trial was carried out using a convenience sample identified from a target population of 12,149 adult cigarette smokers in the general population. Of the 2095 smokers who were enrolled in the study, 95% completed the trial. Participants were randomly assigned to receive on their cigarette packs for 4 weeks either text-only warnings or picture warnings. The outcome variable was attempting to quit smoking during the study, which was identified by using an interview-administered survey given at the start of the study and in week 4. All interviewers were trained on administration of the instrument. Of the participants, 1078 were randomized to the text-only group and 1017 to the picture group. In the analyses, smokers whose packs had pictorial warnings were more likely than those whose packs had text-only warnings to attempt to quit smoking during the 4-week trial (40% vs 34%; 95% CI, 1.09-1.54).

Which issue is the primary concern regarding the internal validity of this study result? and explain why

a.Type 1 error from random error

b.self-selection bias

c.information bias from misclassification of the independent variable

d.precision

e.confounding from unknown factors