Correlation Coefficient

	Consider two samples, say: "liver" and "pooled liver". A correlation coefficient (r) indicates the extent to which the pairs of numbers for these two variables lie on a straight line.
	(fig. 10)
	The correlation for this example is 0.9. If the trend went downward rather than upwards, the correlation would be -0.9. For perfect linearity, r = ±1. If there is no linear trend at all--for example, if there is a random scatter of points--the value of r is close to zero. Points distributed evenly around a circle would also give a correlation of near zero, because there would be no overall linear trend.