presentation econometrics ex 1.pdf
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501 KB
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EX.1
The table below presents data from supermarket on monthly
sales of apples
(
A
,
in tones per month),
average apples prices
(
P
A
, in PLN/kg) and
average
oranges prices
(
P
O
, in PLN/kg) in the period August 2008 – January 2009.
t
A
P
A
P
O
1
6
1
7
2
6
2
6
3
4
3
6
4
3
4
5
5
2
5
4
6
3
5
3
a)
What kind of relationship do You expect between the demand on apples
and the prices of apples and oranges?
When P
A
then A
↑
When P
A
↑
then A
There is negative relationship between the prices of apples and demand on them.
When P
O
then A
When P
O
↑
then A
↑
There is positive relationship between prices of oranges and demand on apples
b)
Estimate parameters of the model:
A = β
0
+ β
1
*P
A
+ β
2
P
0
+ ε
Interpret the results.
6
PA
PO
1
1
7
6
1
2
6
Y =
4
X =
1
3
6
3
1
4
5
2
1
5
4
3
1
5
3
Few steps to estimate parameters:
1. X
T
2. X
T
X
3. det. (X
T
X)
4. (X
T
X)
-1
5. X
T
Y
6. b=(X
T
X)
-1 *
X
T
Y
1.
X
T
=
1
1
1
1
1
1
1
2
3
4
5
5
7
6
6
5
4
3
X
T
X =
6
20
31
2.
20
80
92
31
92
171
3. det. (X
T
X)
0
The result is 96 so it’s okay.
4.
(X
T
X)
-1
= 54,3333
-5,9167
-6,6667
-5,9167
0,6771
0,7083
-6,6667
0,7083
0,8333
5.
X
T
Y =
24
67
134
6. b= (X
T
X)
-1 *
X
T
Y
b =
14,25
-1,71875
-0,875
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