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Table 3 Comparison of trematode infections by statistical methods

From: Estimating trematode prevalence in snail hosts using a single-step duplex PCR: how badly does cercarial shedding underestimate infection rates?

 

Parasite species

Classical method detection

Duplex PCR detection

McNemar

Cohen’s Kappa

+

-

X2-test

P-value

K

P-value

Ebro samples

2011

C. labracis

+

30

7

6.76

0.01

0.37

<0.001

  

-

22

30

  

M. obovata

+

24

4

3.06

0.08

0.61

<0.001

  

-

12

49

  

Double infection

+

3

5

18.27

<0.001

-0.01

0.53

  

-

32

49

 

2013

C. labracis

+

49

0

63.02

<0.001

0.33

<0.001

  

-

65

54

  

M. obovata

+

11

5

2.72

0.1

0.49

<0.001

  

-

13

139

  

Double infection

+

3

1

12.5

<0.001

0.22

0.13

  

-

17

147

Otago samples

LP

M. novaezealandensis

+

87

1

11.53

<0.001

0.78

<0.001

  

-

16

57

  

Philophthalmus sp.

+

16

1

3.13

0.08

0.77

<0.001

  

-

7

137

  

Double infection

+

6

1

2.29

0.13

0.61

0.003

  

-

6

148

 

OB

M. novaezealandensis

+

62

1

19.36

<0.001

0.6

<0.001

  

-

24

39

  

Philophthalmus sp.

+

4

0

4.17

0.04

0.55

0.02

  

-

6

116

  

Double infection

+

0

1

0.8

0.37

-0.01

0.51

  

-

4

121

  1. Comparison of trematode infections in snails detected by the classical method (emission of parasites) and the duplex PCR method. i) Ebro samples: C. labracis, M. obovata and double infections in G. adansonii, from the Ebro Delta (Spain), years 2011 and 2013; and ii) Otago samples: M. novaezealandensis, Philophthalmus sp. and double infections in Z. subcarinatus, from Otago Habour (New Zealand), sampling sites (LP: Lower Portobello Bay, OB: Oyster Bay). Data transformed in two-dimensional contingency tables (2×2). Results from McNemar’s Chi-squared test for paired proportions (χ2) and Cohen’s Kappa Statistic (K) for agreement between both methods. Kappa values can range from <0 (no agreement) to 1 (perfect agreement).