Bias in counting procedures for white blood cells.

To increase the precision of low white blood counts with traditional counting procedures often an initial count is performed in 0.1 cu. mm. Only if this pilot count is low, additional zones of 0.1 cu. mm. are counted and the results of the pilot count and the additional count then averaged. This counting procedure should be avoided as it gives biased estimates of the white blood count. The bias is avoided if the result of the initial count is discarded and an independent count is performed in a larger volume. In analogous counting situation-such as radioactivity counts - bias can arise and be prevented in analogous ways.