A number of factors may affect the validity of allocation models similar to Approach 2. Self-report errors or sampling error may affect validity.
Numerical results demonstrate the validity of the allocation strategy and conclusion arrived in this study, but we do not find the similar arguments in the literature so far, for comparison with the conclusion of this study.
We assessed three key domains of internal validity, concealment of allocation, blind adjudication of outcomes, and the inclusion of all randomised participants in the analysis according to the intention to treat principle (see supplementary appendix).
The validity of the proposed power allocation strategy under various channel link conditions is demonstrated by means of numerical simulations.
In the present study, the validity of the applied group allocation was confirmed by the histological examinations of endometrium biopsies because cows in group M had a higher prevalence of endometritis in the second and third postpartum estrus compared to cows in group H.
Building on previous research around methodological quality of RCTs [ 4, 5], the Cochrane Collaboration recently introduced a tool designed to appraise ROB, encompassing six domains related to the internal validity of a trial: sequence generation, allocation concealment, blinding, incomplete outcome data, selective outcome reporting, and "other" potential threats to validity [ 3].
The methodological aspects assessed in reviews most often pertained to study design, appropriateness of allocation procedures, comparability of groups, validity of assessment and attrition, but only a few reviewers examined additional aspects such as quality of implementation.
However, the internal validity of RCTs is largely dependent on appropriate randomization, allocation concealment, blinding, and strict adherence to eligibility criteria.
The risk of bias tool in Cochrane reviews of randomised trials is routinely used to assess essential items pertaining to validity of trial design such as random sequence generation, allocation concealment, attrition and performance biases.
Only 37% of the participants who volunteered to take a guess were able to correctly identify their treatment allocation, suggesting that the internal validity of the trial findings were unaffected by a breech in the trial blinding.
