Table 2.

Data on the statistical strength of the correlations between the physicochemical aspects of the coal (data from the USGS) and the CWP prevalence rates obtained from the NSCWP 1970 survey presented in Huang et al. (2005)

Physicochemical aspect	Correlation coefficient (r)	95% confidence interval	P value
BAI	0.94	0.66 to 0.999	0.0015
Spy	0.91	0.35 to 0.99	0.0048
FeT	0.85	0.20 to 0.97	0.016
Coal rank	0.59	0.26 to 0.91	0.16
Quartz	0.28	0.55 to 0.82	0.54
Calcite	− 0.18	− 0.78 to 0.60	0.69
*BAI low pH	0.90	0.40 to 0.99	0.006
*BAI buffered pH	0.87	0.25 to 0.98	0.01

S_py, pyritic sulphur; Fe_T, total iron

^*Low pH, assuming no neutralisation by calcite, high pH, accounting for acid neutralised by calcite

All significant relationships are indicated in bold (P value < 0.05)