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Birthweight(gms)
BPD N Prop.
0-950 49 68 0.721
951-1350 18 80 0.225
1351-1750 9 75 0.120
Total 76 223 0.341
BPD (Bronchopulmonary Dysplasia) by birth weight
Proportion of BPD decreases with birthweight.
Q: Can we give a more precise functional form to the relationship between the probability of having BPD and birthweight? Ans: Yes, if exact birthweights rather than birthweight categories are recorded.
By fitting a logistic regression model to the dichotomous response BPD.
BPD
No BPD
Dichotomous Outcomes
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Logistic regression of BPD on birthweight
Logit estimates Number of obs = 223
W = 62.42 (df=1)
p value = 0.0000
Log likelihood = -111.86031
-----------------------------------------------------------------------------------------
BPD | Coef. Std. Err. z P>|z| [95% Conf. Interval]
---------+-------------------------------------------------------------------------------
birthwt | -.0042291 .0006409 -6.599 0.000 -.0054852 -.0029731
_cons | 4.034291 .6957847 5.798 0.000 2.670578 5.398004
------------------------------------------------------------------------------------------
Logistic regression of BPD on birthweight
Logit estimates Number of obs = 223
W = 62.42 (df=1)
p value = 0.0000
Log likelihood = -111.86031
------------------------------------------------------------------------------
BPD | Odds Ratio Std. Err. z P>|z| [95% Conf. Interval]
---------+--------------------------------------------------------------------
birthwt | .9957798 .0006381 -6.599 0.000 .9945298 .9970313
------------------------------------------------------------------------------
bwtp
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model logistic Fitted
Birthweight(gms)
ObsrvdBPD
FittedBPD
N
0-950(750) 0.721 0.708 68
951-1350(1150)
0.225 0.311 80
1351-1750(1550)
0.120 0.078 75
Total 223
Observed versus fitted