Table 3. Correlations between intensity, duration, frequency, volume and index.

		Intensity	Duration	Frequency	Volume	Index
Intensity	R		0.70	0.67	0.59	0.76
	P		<0.001	<0.001	<0.001	<0.001
Duration	R	0.70		0.89	0.91	0.79
	P	<0.001		<0.001	<0.001	<0.001
Frequency	R	0.67	0.89		0.97	0.86
	P	<0.001	<0.001		<0.001	<0.001
Volume	R	0.59	0.91	0.97		0.89
	P	<0.001	<0.001	<0.001		<0.001
Index	R	0.76	0.79	0.86	0.89
	P	<0.001	<0.001	<0.001	<0.001