Effectiveness of Air Filters in Allergic Rhinitis: A Systematic Review and Meta-Analysis

Table 2

Summary of the risk of bias.

Study	Year	Study design	D1	DS	D2	D3	D4	D5	Overall
Park et al. [34]	2020	RCT parallel	Low		Low	Low	Low	Low	Low
Li et al. [33]	2020	RCT parallel	Some concerns^†		Low	Low	Low	Low	Some concerns
Wood et al. [32]	1998	RCT parallel	Some concerns^†		Low	Low	Low	Some concerns^‡‡	Some concerns
Brehler et al. [31]	2003	RCT crossover	Low	Some concerns^§	Low	Low	Low	Some concerns^‡‡	Some concerns
Stillerman et al. [35]	2010	RCT crossover	Low	Low	Low	Low	Low	Low	Low
Antonicelli et al. [16]	1991	RCT crossover	Some concerns^†	Some concerns^§	Some concerns^¶	Low	High^††	Some concerns^‡‡	High
Reisman et al. [17]	1990	RCT crossover	Some concerns^†,‡	Low	Low	Low	Low	Some concerns^‡‡	Some concerns
Kooistra et al. [24]	1978	RCT crossover	Some concerns^†,‡	Some concerns^§	Low	Low	Low	Some concerns^‡‡	Some concerns

D1: randomization process; DS: bias arising from period and carryover effects; D2: deviations from the intended interventions; D3: missing outcome data; D4: measurement of the outcome; D5: selection of the reported result. ^†Lack of description of the allocation concealment methods. ^‡Lack of baseline information of two groups after randomization. ^§Lack of washout period. Lack of sufficient time passes before outcome measurement in the second period for any carryover effects to have disappeared. ^¶Participants aware of their assigned intervention during each period of the trial. ^†† Outcome assessors aware of the intervention received by study participants and influenced by knowledge of intervention received. ^‡‡Lack of prespecified plans.