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Table 2 Risk of bias of studies included in this meta-analysis

From: The efficacy of vitamin D supplementation for irritable bowel syndrome: a systematic review with meta-analysis

Study Random sequence generation Allocation concealment Blinding of participants, personnel Blinding of outcome assessment Incomplete outcome data Selective reporting Other sources of bias
Abbasnezhad 2016 [23] Low risk; computer-generated blocked randomization list with a block size of 6 Low risk; quote "all the participants, researchers, and the physician were blind to the allocations using the random codes" Low risk, double-blind Low risk, double-blind Low risk, quote "All analyses were done on the intention-to-treat population" Low risk, all prespecified outcomes were reported Low risk
Khalighi Sikaroudi 2020 [24] Low risk; randomization was performed by using the online site www. sealedenvelope.com Low risk; quote "For performing the concealment in the randomization process, dedicated codes were used on the pharmaceutical sheets, which were generated by the software." Low risk, double-blind Low risk, double-blind Low risk, intention-to-treat analysis Low risk, all prespecified outcomes were reported Low risk
El Amrousy 2018 [25] Low risk; quote "computer-generated random numbers using a random block size of 6" Low risk; quote "Allocation concealment was done by sequentially numbered sealed opaque envelopes." Low risk; participants and treating staff were blinded to the treatment group. Low risk; all outcome assessors were blinded to the treatment group Low risk, complete outcome Low risk, all prespecified outcomes were reported Low risk
Jalili 2016 [26] Unclear; the author reported that participants were randomly assigned to different groups but did not mention how the random sequence was generated Low risk; randomization was provided in sealed opaque envelopes with successive numbers. Low risk; all participants and researchers were blinded to the treatment group. Unclear; insufficient information Low risk, intention-to-treat analysis Low risk, all prespecified outcomes were reported Low risk