^ log(bwght) = 4.66 - .0044 cigs + .0093 log( faminc) + .016 parity (.22) (.0009
ID: 2507288 • Letter: #
Question
^log(bwght) = 4.66 - .0044 cigs + .0093 log( faminc) + .016 parity
(.22) (.0009) (.0059) (.006)
+ .027 male + .055 white
(.010) (.013)
n = 1,388, R ^ 2 = .0472
and
^ log(bwght) = 4.65 - .0052 cigs + .0110 log( faminc) + .017 parity
(.38) (.0010) (.0085) (.006)
+ .034 male + .045 white - .0030 motheduc + .0032 fatheduc
(.011) (.015) (.0030) (.0026)
n = 1,191, R^2 = .0493.
The variables are defined as in Example 4.9, but we have added a dummy variable for whether
the child is male and a dummy variable indicating whether the child is classified as white.
(i) In the first equation, interpret the coefficient on the variable cigs. In particular, what
is the effect on birth weight from smoking 10 more cigarettes per day?
(ii) How much more is a white child predicted to weigh than a nonwhite child, holding
the other factors in the first equation fixed? Is the difference statistically significant?
(iii) Comment on the estimated effect and statistical significance of motheduc.
(iv) From the given information, why are you unable to compute the F statistic for joint
significance of motheduc and fatheduc? What would you have to do to compute the
F statistic?
Explanation / Answer
i)the coefficient on the variable cigs can be interpreted as if cigs changes by 1 unit then percentage change in birth weight decreaes by 0.44% as its coefficient is )-0.0044)
if there is smoking 10 more cigarettes per day , then birth weight decreasesby 10*-0.0044
=-0.044
=-4.4%
so birth weight decreases by 4.4% if there is smoking 10 more cigarettes per day
ii)holding the other factors in the first equation fixed, white child will be 0.45 more than non white child as summy variable coefficient of white is 0.45
Yes, difference is statistically significant as its p-value is 0.015 which is less than 0.05
iii) if motheduc changes by 1 unit, then percentage change in birth weught decraeses by 0.35 . As its coefficent is -0.003
and it have significant effect as its p-value is also 0.0030 which is less than 0.05
iv)We will bne unable to compute the F statistic for joint significance of motheduc and fatheduc as we dont know the partial correlation coefficent between these two variables motheduc and fatheduc.
To compute F-stat , first we need the value of partial correlation coefficent between two variables motheduc and fatheduc and also as degrees of freedom is known
we can compute the F-statistic
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