Online self-study of chest X-rays shows no difference between blocked and mixed practice

Chest radiograph interpretation is a complex skill and learners may benefit from deliberate instructional design modalities, such as mixed practice. Proposed benefits of mixed over blocked practice include the elimination of cueing and the highlighting of contrasting features. However, current evidence for the superiority of mixed practice is conflicting.

This study compares mixed versus blocked practice, after the initial teaching of concepts, among medical students using online self-study chest X-ray (CXR) modules.

Two online CXR modules were developed that cover identical content but differ in the organisation of practice images. Blocked modules provided practice CXRs after each category, whereas mixed modules randomly ordered practice radiographs after all categories had been taught. Medical students in Years 1-3 were randomised to either module and were tested on 20 new CXRs immediately after completion and at 2 weeks. The primary outcome was immediate diagnostic accuracy. Secondary outcomes included diagnostic accuracy at 2 weeks, time per module and reported module difficulty.

A total of 58 medical students participated (32 in the blocked and 26 in the mixed module). Level of training and previous CXR experience were similar across the groups. Totals of 1160 and 1120 answers were evaluated for immediate and 2 week post-test scores, respectively. There were no significant differences in mean diagnostic accuracy between the blocked (mean score: 11.7/20) and mixed (mean score: 11.0/20) practice groups on immediate testing (t = 0.83, d.f. = 56, p = 0.41) or at 2 weeks (mean score: 11.2/20 versus 10.9/20; t = 0.518, d.f. = 54, p = 0.61). Post-test scores showed no correlation with training level (R = 0.23, p = 0.09) or completion time (R = -0.09, p = 0.5). Reported module difficulty was similar between the mixed (3.22/5) and blocked (3.19/5) groups. On multivariable linear regression controlling for completion time, training level and CXR experience, between-group differences remained non-significant.

Performance after mixed practice was similar to that after blocked practice. Results may reflect similarities between modules in teaching, which emphasised contrast learning, greater effect of initial teaching rather than practice, or absence of tutor-led instruction. Alternatively, results may reflect the higher cognitive load in mixed practice imposed by contrasting multiple diagnoses.