birthweight (gms) bpdnprop. 0-95049680.721 951-135018800.225 1351-17509750.120 total762230.341 bpd...
DESCRIPTION
BPD No BPD Dichotomous OutcomesTRANSCRIPT
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
In linear regression, continuous Y:
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Logistic regression of BPD on birthweight
Logit estimates Number of obs = 223 W = 62.42 (df=1) p value = 0.0000Log 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------------------------------------------------------------------------------
bwtpp 0042.00343.4
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Birthweight(gms)
ObsrvdBPD
FittedBPD N
0-950(750) 0.721 0.708 68951-
1350(1150) 0.225 0.311 801351-
1750(1550) 0.120 0.078 75
Total 223
Observed versus fitted