I have written frequently about correlations (See my post of Feb.13, 2008: correlations with 16 references.). What I haven’t explained is how to find out whether a correlation is one that you can rely on.
The statistician’s term is “statistically significant,” a standard that has three components. To explain them let’s start with a correlation, such as between median partner hourly rates and median associate hourly rates. You collect that data for 20 law firms, enter it into a spreadsheet, and use a built-in function to calculate the correlation between the two sets of figures. The correlation is 0.45. How confident can you be that the correlation really means something and isn’t just some chance finding? I found a very clear explanation online of statistical significance and tinkered with it.
The easiest way to find out is to look in a statistics book that has a table of critical values of r (the correlation figure, here 0.45). You need to decide on a significance level, which is commonly called alpha and set at .05. This means that the odds that the correlation is a chance occurrence are no more than 5 out of 100.