Scatterplot

http://www.uv.es/prodat/ViSta/vista-frames/help/lecturenotes/lecture11/weight&horses-scatterplot.gif

Scatter plots depict the realtionship between two variables; in this case, automobile weight and horsepower. If a trendline is placed inside based on the means of the data, one can tell if the relationship is positive (both variables are increasing) or negative (one variable increase and one decreases). In this plot, there is a positive relationship. Using statistics, the amount of the relationship can be determined (correlation), but correlation does not mean there is "causation".