Scatter Plots
Find the line of best fit.
Focus 7 - Learning Goal #2: The student will construct, interpret and
identify patterns of associations for bivariate data displayed in two-way tables
and scatterplots.
4
In addition to
level 3.0 and
beyond what was
taught in class,
the student
may:
 Make
connection
with other
concepts in
math.
 Make
connection
with other
content
areas.
3
The student will
construct,
interpret and
identify patterns
of associations for
bivariate data
displayed in twoway tables and
scatterplots.
- Write equation
of line-of-best-fit.
And use it to
make predictions.
- Calculate
relative
frequencies and
describe their
meaning.
2
The student will
construct
scatterplots and
two-way tables
from bivariate
data.
- Draw line-ofbest-fit for scatter
plot.
- Identify patterns
of associations.
- Able to
generally describe
relationship of
bivariate data
displayed in a
two-way table.
1
With help from
the
teacher, the
student has
partial success
with level 2 and
3 elements.
0
Even with help,
students have no
success with
investigating
patterns of
association with
bivariate data.
• Scatter plots show relationships between two sets of data.
• If there is a relationship between the two sets of data, we
need to draw in a “Line of Best Fit”
• This is a line that is the line that comes closes to all of the
dots on the graph. However, it does not touch all of the
dots.
• If the dots are close to the line, the graph has a strong
correlation.
• If the lines are further from the line, the graph has a weak
correlation.
Line of Best Fit
• Use the data on the price per ticket and how many tickets
were sold to create a scatter plot.
Create a Scatter Plot
Ticket Price and Sales
Number of Tickets Sold
• This is a scatter plot for
ticket sales for a school
play.
• This shows the
relationship between
ticket price and how
many tickets were sold.
• Place a ruler on the
graph. Try to get it to
touch as many points as
possible. Try to have an
equal number of points
above and below the
line.
• Then draw a line.
• This is the “Line of Best
Fit” for this graph.
10
8
6
4
2
0
0
5
10
Cost Per Ticket
15
Is this a strong or weak correlation?
• What information do we need
in order to write an equation of
a line?
• y = mx + b
• We need a slope and a
y intercept.
• How do find the y-intercept?
• Where does your line cross the
y-axis?
• About (0, 10)
Write the equation of the
line of best fit.
• How do we find slope?
• Pick two points that touch
the line that are far apart.
• The ordered pairs are
listed in your table of
data.
• (2, 8) & (10, 3)
• 3 – 8 = -5
10 - 2
8
Write the equation of the
line of best fit.
• We have a y-intercept (0, 10).
• We have a slope of -5/8.
• We can substitute that
information into the equation
y = mx + b.
• Remember m is the slope and
b is the y-intercept.
• The equation of the line of
best fit is:
y = -5/8x + 10
Write the equation of the
line of best fit.
• The circus performs 10 times.
Each time they keep data on the
number of water bottles and
lunch boxes sold.
• Use the data provided to make a
scatter plot.
• Draw the line of best fit.
• Write the equation of the line
of best fit.
Try it again…
•
•
•
•
•
•
Draw the line of best fit.
Find the y-intercept.
About (0, 85)
Find the slope.
(20, 67) & (58, 34)
34 – 67 = -33
58 – 20
38
• y = mx + b
• y = -33/38x + 85
Is this a strong or weak correlation?
Write equation of line of best fit.