Scatter Plots


Math A	Scatter Plots

Have you ever been curious to know if one event affects another event?

For example, if I study longer, will I get a better grade on my Regents examination?

Statisticians and quality control technicians gather data to determine correlations (relationships) between such events. Scatter plots will often show at a glance whether a relationship exists between two sets of data.

Let's decide if studying longer will affect Regents grades based upon a specific set of data. Given the data below, a scatter plot has been prepared to represent the data. Remember when making a scatter plot, do NOT connect the dots.

Study Hours	Regents Score
3	80
5	90
2	75
6	80
7	90
1	50
2	65
7	85
1	40
7	100

Notice: Certain values may have more than one result,
such as (7,90) and (7,85) and (7,100).

The data displayed on the graph resembles a line rising from left to right. Since the slope of the line is positive, there is a positive correlation between the two sets of data. This means that according to this set of data, the longer I study, the better grade I will get on my Regents examination.

Note: Just because this set of data showed a positive correlation does not mean that the relationship is positive for all sets of data. There may be sets of data that show that there is NOT a positive correlation between hours studying and better Regents scores. It all depends on the data being examined.

If the slope of the line had been negative (falling from left to right), a negative correlation would exist. Under a negative correlation, the longer I study, the worse grade I would get on my Regents examination. YEEK!!

If the plot on the graph is scattered in such a way that it does not approximate a line (it does not appear to rise or fall), there is no correlation between the sets of data. No correlation means that the data just doesn't show if studying longer has any affect on Regents examination scores.

How to use your
TI-83+ graphing calculator with scatter plots.
Click calculator.

Roberts