1. What every good graph needs…
PLM – Unit 1

2. Graphing Vocab
X-axis: The horizontal line on a graph (runs left and right)
Y-axis: The vertical line of a graph (runs up and down)
Best fit line: A line that follows the trend of the majority of data points
Slope: Rise over Run (how steep is the angle on a linear graph?)
Y intercept: The value of “y” where the line crosses the y-axis

3. Graphing Vocab
X-axis: The horizontal line on a graph (runs left and right)
Y-axis: The vertical line of a graph (runs up and down)

4. Graphing Vocab
Best fit line: A line that follows the trend of the majority of data points
Questions to ask about your best fit line:
Does the line follow the distribution of the data points
As you move along the x-axis, do the points seem to increase in value (be higher along the y-axis)?
Do they decrease?
Is there some other pattern?

5. Graphing Vocab
Best fit line: A line that follows the trend of the majority of data points
Do you have approximately the same number of data points above and below the line?
Are the points evenly distributed along the line?
You don’t want all the points above the line to be at the low end of the x-axis or…
…all the points below the line to be at the high end of the x-axis.

6. Graphing Vocab
Best fit line: A line that follows the trend of the majority of data points
It might be a straight line:

7. Graphing Vocab
Best fit line: A line that follows the trend of the majority of data points
It could be a curved line, depending on the data points

8. Graphing Vocab
Which line do you think is the best “best fit line” for this graph?
Sometimes you will need more information to in order to decide.

9. Graphing Vocab Slope: Rise over Run (how steep is the angle?)
On a straight line graph it is calculated using the formula: example:

10. Graphing Vocab
Y intercept: The value of “y” where the line crosses the y-axis
For the general formula, y = mx + b, “b” is the y intercept

11. DAT Rule D = Data points A = Axes...straight and labeled!
T = Title...make it descriptive
R = Ruler...use one!
U = Units on the axes
independent (manipulated) variable goes on the x-axis
dependent (responding) variable goes on the y-axis
L = Labels on the axes (inc. units)
E = Even # intervals on the axes

12. Where do the data points come from?
Graphing is a form of analysis. The original raw data needs to be organized into an x-y table (or t-table) so that you may easily create the graph.
From the x-y table you can decide how your axes will be scaled (numbered) and labeled.
Here is a sample x-y table:
The graph is next.
The Effect of Automobile Speed on Traffic Ticket Cost
(MV)
Automobile speed (kph)
(x)
(RV)
Cost of average speeding ticket (dollars) (y) 11 40 24
100 39 80 50
130 64 90 78
160 83
135 97
220
MV goes on the x-axis
RV goes on the y-axis
Notice MV values increase from top to bottom (they are orderly).

13. Is this a good graph?
Looking at your DAT Rule, identify (circle, highlight, etc) each component of a good graph.