Drug Abuse

A Note to the Non-Scientist Reader

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In order to conveniently present exact findings to the researchers who read this book, there are lots of parentheses filled with numbers and simple statistics.
If you aren't interested in the exact findings, or if numbers and statistics turn you off, there's a simple way to avoid any problem: ignore them. Everything has been written in plain English, and the numbers confined to parentheses for just this reason!
If, on the other hand, you haven't a formal background in statistics but would like to know what the probability figures in the parentheses (such as "p < .05") mean, it all boils down to this: how do you know when a difference in the way two groups of people answer a question is a meaningful, significant difference, and how do you know when it results only from the random variation you get whenever you deal with people's responses?
You never know for certain which is which, but a statistical test is an objective way of being reasonably sure, one way or the other. Statistical tests use the known mathematical properties of numbers to let you decide when a difference is probably due to chance, and when a difference is so large that chance seems unlikely. The exact mathematics aren't of interest to the general reader, but only the outcome, the probability figure. If the outcome of a particular test could have happened by chance only five or fewer times in a hundred trials (conventionally expressed in this book as p<.05, probability equal to or less than 5/100),* we begin to doubt that this is chance variation. It probably represents a real difference between the groups. If the probability is even smaller that the outcome is due to chance, say less than one in a hundred (p < .01) or less than one in a thousand (p < .001), we can feel quite certain that we are dealing with real, important differences.**
Thus in this book the lower the probability figure in parentheses, the greater the difference between the groups being compared.

 

Footnotes

*More exactly, the sign should be [less than or equal to] rather than simply <, but this simplification will be used throughout the text.
**Statistical tables available to me only go up to the .0005 level. When I use the notation p << .0005, the difference is even more significant; when I use p <<< .0005, it is supersignificant. For the technically minded, I use p << .0005 when chi square is greater than or equal to 50, and p <<< .0005 when chi square is greater than or equal to 100, with four degrees of freedom in each case.

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