Question
Based on quarterly observations for the U.S. for the period 1961-I through 1977-II, economists estimated the following demand function for coffee. The figures in parentheses
Based on quarterly observations for the U.S. for the period 1961-I through 1977-II, economists estimated the following demand function for coffee. The figures in parentheses are t-values. (note: t = B/se). R2 = 0.80.
ln(Qt) = 1.2789 - 0.1647 ln(Pt) + 0.5115 ln(It) + 0.1483 lnP't - 0.0089T - 0.0961 D1t - 0.1570D2t - 0.0097D3t
(-2.14) (1.23) (0.55) (-3.36) (-3.74) (-6.03) (-0.37) ...where:
Q = pounds of coffee consumed per capita P = the relative price of coffee per pound at 1967 prices
I = per capita personal disposable income, in thousands of 1967 dollars
P' = the relative price of tea per quarter pound in 1967 prices
T = quarterly time trend with T=1 for 1961-I, to T=66 for 1977-II
D1 = 1 for the first quarter of the year D2 = 1 for the second quarter of the yearD3 = 1 for the third quarter of the year
- How would you interpret the coefficients on ln(P), ln(I), and ln(P')?
- Is the demand for coffee price elastic? Explain how you know.
- Are coffee and tea substitute or complementary products? How do you know?
- How would you interpret the coefficient on T?
- What is the trend rate of growth or decline in coffee consumption in the United States?
- What is the income elasticity of demand for coffee?
- Test the hypothesis that the income elasticity of demand for coffee is not significantly different from 1.
- How do you interpret the coefficients on D1, D2, and D3?
- Which of the dummies are statistically significant?
- Is there a pronounced seasonal pattern in coffee consumption? If so, what is the pattern?
- Which is the benchmark quarter in this example? How would the results change if the benchmark quarter were changed to the quarter before this?
- This model only includes the differential intercept dummies. What implicit assumption is being made here?
- How would you re-write the model to take into account differential slope dummies?
- Suppose you are asked to forecast for the next period after the end of the sample, 1977-III. Suppose that in this quarter, the price of coffee is $5, the price of tea is 3, and income is 15,000. What is your forecasted value? What is your 95% confidence interval around that value? (Note: forecast the ln(Q) and its interval, then take the inverse-logs of these values to put your forecast in terms of pounds of coffee demanded.) To answer this, assume the standard error of the regression is 0.4.
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