TABLE 4 CONFIDENCE LIMITS AS A PERCENT OF MEAN CONCENTRATION BASED ON ASSUMED COEFFICIENT OF VARIATION OF 0.7 NUMESR OF SAMPLES PROBABLE ERROR STRATIFICATION MEAN CONCENTRATION PER + % of 5 63 10 dd 20 31 30 26 20 20 60 18 ho 22. 1h . 100 200 10 500 6.3 1000 kok Confidence Limit = PE, = 2(0.7) vn (as a proportion of the mean) 4/