220.127.116.11.2 Avoidance of Bias
If possibilities of bias exist, fully objective conclusions cannot be drawn. The first essential of any sampling or census procedure must, therefore, be the elimination of all sourced of bias. The simplest and the only certain way of avoiding bias in the selection process is for the sample to be drawn either entirely at random, or at random subject to restrictions which, while improving the accuracy, are of such a nature that they do not introduce bias in the results. In certain cases, systematic selection may also be permissible.