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Table 5 Output parameters of the a priori power analysis computation process at varying the α (0.10; 0.05; or 0.01)

From: Validating the regional estimates of changes in soil organic carbon by using the data from paired-sites: the case study of Mediterranean arable lands

α

0.10

0.05

0.01

Raw data

 Noncentrality parameter δ

2.6008000

2.9077828

3.5612921

 Critical t

1.7174255

2.0495831

2.6981518

 Degrees of freedom

21.9183118

27.6478898

41.9718346

 Minimum sample size needed

24

30

45

 Actual power

0.8090485

0.8010923

0.8005742

log10 data

 Noncentrality parameter δ

2.6384055

3.0465682

3.6685540

 Critical t

1.7676466

2.1001020

2.7730806

 Degrees of freedom

13.3239449

18.0985932

26.6929601

 Minimum sample size needed

15

20

29

 Actual power

0.8040250

0.8216418

0.8056966

  1. The process was carried out through the G-Power software with the Wilcoxon test for non-normal distributed datasets [65]. Input data were from 302 measured samples of SOC in 1994 and modelled SOC in 2008, each of which expressed as either raw or log10 data. Minimum power was set to 0.80