We have previously described three general domains of statistics: differences between groups; association between groups; and time-to-event (survival) data. This article will describe the statistics commonly used in these last two domains: associations between groups; and survival data.
We would likely find that as we spent more time on our cell phone, our phone bill would increase. If for every additional minute our bill increased by exactly the same amount, we would have perfect positive correlation, with a correlation coefficient of 1, and all the data points would lie on the diagonal line. What is more likely is that we will not have perfect correlation, and the data points will be scattered on either side of the line. The closer the points are to the line, the stronger the correlation, and the higher the correlation coefficient. The correlation coefficient takes values between -1 and 1. A value of -1 means perfect negative correlation (ie every increase in x leads to an exact decrease in y) with 0 being the null value.
