CHAPTER 8

Kalra7 carried out an inter-laboratory collaborative trial of methods for the determination of the pH of soils. Fifty-three laboratories were involved in the study and they each measured 10 blind duplicate samples of different soils using several methods. The data presented in Table 8.3 are the pH measurements of Malbis soil samples for the first 20 laboratories, using a single method.

Table 8.3: Duplicate pH measurements of a soil by 20 laboratories ( *Reprinted from the Journal of AOAC INTERNATIONAL, 1995, Vol. 78, pp 310. Copyright, 1995, by AOAC INTERNATIONAL*).
Lab	pH		Lab	pH
1	5.90	5.95	11	4.92	5.46
2	5.48	5.69	12	5.40	5.49
3	5.50	5.50	13	6.29	6.54
4	5.45	5.52	14	5.65	5.73
5	5.37	5.59	15	5.45	7.10
6	5.18	5.57	16	5.55	5.82
7	5.46	5.53	17	5.42	5.33
8	5.64	5.84	18	5.46	5.57
9	5.30	5.20	19	4.95	5.18
10	5.86	6.14	20	5.51	5.89

Answers

The table below gives the ANOVA analysis of the Kalra data, including estimates of the repeatability standard deviation (error) and reproducibility standard deviation (total).

Analysis of Variance for pH
Source	DF	SS	MS	F	P
Lab	19	4.3736	0.2302	2.444	0.027
Error	20	1.8834	0.0942
Total	39	6.2570
Variance Components
Source	Var Comp.	% of Total	StDev
Lab	0.068	41.93	0.261
Error	0.094	58.07	0.307
Total	0.162		0.403

2.	Apply Cochran's test to the...

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