Table 6 Goodness-of-fit Chi (χ2) square model inputs.

From: A reliable model to strengthen community-based water quality monitoring and surveillance via field test kits

Concentration (µg/L) range

AsKit-1 results (No. of samples)

AAS-HG results (No. of samples)

Observed frequency (O)

Expected value (E)

Observed frequency (O)

Expected value (E)

 < 10

28

28.82

30

29.18

 ≥ 10 < 20

19

19.87

21

20.13

 ≥ 20 < 50

10

8.45

7

8.55

 ≥ 50 < 100

22

21.86

22

22.14

  1. Number of categories (k) = 8; Sample size (n) = 159; Degree of freedom (df) = 7; Chi (χ2) Square = \(\sum\nolimits_{{{\text{i}} = 1}}^{{\text{n}}} {\frac{{\left( {{\text{O}}_{{\text{i}}} - {\text{E}}_{{\text{i}}} } \right)}}{{{\text{E}}_{{\text{i}}} }}}\)  = 0.6891; Phi (φ) effect = \(\sqrt {\frac{{{\upchi }^{2} }}{{\text{n}}}}\)  = 0.06583.
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