“… Funnel plot of this meta-analysis. The symmetry of the graph is represented by the proportional and relatively well-distributed division on both sides of the horizontal axis of the circles in its plane [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 ]. …”