Table 3. Statements for which the differences in the responses of the ECR and PI populations were statistically significant.

We calculated the mean degree of agreement by setting 1 as Strongly Agree through to 5 as Strongly Disagree, and 3 set as No Opinion. The higher the mean value calculated for the group, the closer the group feels to disagreeing with statement. “No opinion” responses, coded as 3, are included in these means. A 2-tailed student’s t-test for equality of the means was used to calculate p values. Due to the difference in the percentage of ECRs and PIs with "no opinion" for the third question, we removed "no opinion" responses and recalculated the mean scores: the difference between the mean scores was reduced but remained significant (ECRs: 1.57 ± 0.05 (n = 365); PIs: 1.88 ± 0.15 (n = 64); p=0.048).

Statement	ECR Mean Score	PI Mean Score	p value	% ECRs with no opinion	% PIs with no opinion
Involving members of a research group in peer review is a beneficial training exercise.	1.32 ± 0.03 (n = 405)	1.54 ± 0.10 (n = 81)	p=0.033	2.5	2.5
It is ethical for the invited reviewer (e.g. PI) to involve others (e.g. their trainees) in reviewing manuscripts.*	2.06 ± 0.06 (n = 406)	2.37 ± 0.14 (n = 81)	p=0.029	11	15
It would be valuable to have my name added to a peer review report (e.g. to be recognized as a co-reviewer by the editor; or to use a service such as Publons to be assigned credit).	1.71 ± 0.05 (n = 405)	2.11 ± 0.13 (n = 81)	p=0.003	10	21

*Indicates that p value was calculated assuming equal variance according to Levene’s test for Equality of Variances.