Databases Reference
In-Depth Information
Here the little “hat” symbol on top of the
β
is there to indicate that it's
the
estimator
for
β
. You don't know the true value of
β
; all you have is
the observed data, which you plug into the estimator to get an estimate.
To actually fit this, to get the
β
s, all you need is one line of R code where
you've got a column of y's and a (single) column of x's:
model <- lm(y ~ x)
So for the example where the first few rows of the data were:
x
y
7
276
3
43
4
82
6
136
10
417
9
269
The R code for this would be:
>
model
<-
lm
(
y
~
x
)
>
model
Call
:
lm
(
formula
=
y
~
x
)
Coefficients
:
(
Intercept
)
x
-32.08
45.92
>
coefs
<-
coef
(
model
)
>
plot
(
x
,
y
,
pch
=
20
,
col
=
"red"
,
xlab
=
"Number new friends"
,
ylab
=
"Time spent (seconds)"
)
>
abline
(
coefs
[
1
],
coefs
[
2
])
And the estimated line is
y
=−32 . 08 + 45 . 92
x
, which you're welcome
to round to
y
=−32 + 46
x
, and the corresponding plot looks like the
lefthand side of
Figure 3-5
.
