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

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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

------------------------------------------------------------------------------

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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