Page 18-54
Example 1 -- For the following (x,y) data, determine the 95% confidence
interval for the slope B and the intercept A
x
2.0 2.5 3.0 3.5 4.0
y
5.5 7.2 9.4 10.0 12.2
Enter the (x,y) data in columns 1 and 2 of ΣDAT, respectively. A scatterplot of
the data shows a good linear trend:
Use the
Fit Data.. option in the ‚Ù menu, to get:
3: '-.86 + 3.24*X'
2: Correlation: 0.989720229749
1: Covariance: 2.025
These results are interpreted as a = -0.86, b = 3.24, r
xy
= 0.989720229749,
and s
xy
= 2.025. The correlation coefficient is close enough to 1.0 to confirm
the linear trend observed in the graph.
From the
Single-var… option of the ‚Ù menu we find: x = 3, s
x
=
0.790569415042,y = 8.86, s
y
= 2.58804945857.
Next, with n = 5, calculate
5.2427905694150.0)15()1(
22
=⋅−=⋅−=
xxx
snS
=−⋅⋅
−
−
= )1(
2
1
222
xyye
rs
n
n
s
...1826.0)...9897.01(...5880.2
25
15
22
=−⋅⋅
−
−
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