They do this by masking disparities in distribution. A Practical Guide , author Brant Houston tells of a San Jose Mercury News story on firefighting response times. The San Jose fire department claimed its average response time was 4.5 minutes, but using a spreadsheet, the reporters calculated that one-fourth of calls were taking longer than the maximum five minutes for firefighters to arrive. This attempts to establish whether there's a relationship between two variables. Age and cancer rates would be a classic.
R is the most important.
R 2 is the coefficient of determination. If R is .5, then R 2 is .25. That means you've eliminated 25 per cent of possible error. If R 2 was 1, you have eliminated all error. Correlation doesn't equal causation.