Scatter diagram

... suppose that we're interested in variables related to a person's extraversion. Our first step is to identify a variable that we think might be related (e.g., number of friends, use of drugs, success in sales, and so forth), and then we examine how the distributions of each of these variables co-vary with one another. By co-vary, I mean, as the values of extraversion go up, the values of other variables go up (or down, depending on the variable in question). Variance measures how much the values of a variable deviate from the mean. Covariance measures how much a pair of variables tend to deviate in the same direction. For example, if we expect that extraversion and cigarette smoking are positively related, we should expect to see that people who score high above the mean on extraversion should also smoke more cigarettes than average. People who score low on extraversion tests should smoke less than average. ...


See the complete article here:
http://my.ilstu.edu/~wjschne/138/Psychology138Lab8.html

---

... Correlation Coefficient, r : The quantity r, called the linear correlation coefficient, measures the strength and the direction of a linear relationship between two variables. The linear correlation coefficient is sometimes referred to as the Pearson product moment correlation coefficient in honor of its developer Karl Pearson...


See the complete article here:
http://mathbits.com/mathbits/tisection/statistics2/correlation.htm

---

Example scatter plot

---

Read the complete articles.

Now answer the following question:
There are many free tools -some are online- that allow us to draw scatter diagrams (true or false). Hint see http://www.xuru.org/rt/LR.asp#CopyPaste

The value r -correlation coefficient- tells us how closely related two variables are? (true or false)