Principle 6 deals with the attribution of causes to effects. It describes the relation
between all causes and probab le causes. This is effectively the expression of circumstantial
evidence, as a probability leading to a conclusion but one less convincing than the
conclusion reached using direct evidence. Principle 7 involves the basis of confidence
limits. To illustrate, if a random sample of 100 variables is taken and is found to have a
mean of 40 and a standar d deviation of 11, it will not be possible to determine a precise
mean. The best that can be established is limits within which the mean will fall with
a specified probability or confidence, usually taken as 95 percent. Again we need to ask
ourselves the question, ‘‘How precise a measurement ...