Dangers of Smoking
ACM 270-1: Introduction to Statistical Inference
Lecture 2b, Jan 6, 2016
Agenda
• Maternal Smoking and Infant Health
• Background
• Data
• Summarizing Data
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Background: Fetal Development
37w
preterm
42w
40w
typical gestation period
brain damage is likely due to
deterioration of the placenta
• Placenta is a special organ that develops during pregnancy
• Transfers
• Nutrients and oxygen from the mother to the fetus
• Waste products and carbon dioxide back to the maternal blood
• Fetus is attached to the placenta by its umbilical cord
• Gestational age is a measure of the baby’s maturity
• Another measure is the birth weight
• Smaller babies and babies born early have lower survival rates
Source: http://cdn.lifemartini.com/wp-content/uploads/2013/05/Placenta-Previa.jpg
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Birth Weight
Babies born at term with weight < 2.5kg are
considered small for their gestational age
4kg
Sophia, Hiking in New England
3.8kg
• Many pregnant women still smoke
• National Center for Health Statistics:
• In 1996: 15% mothers smoked during pregnancy
• In 2013: 8% mothers smoked during pregnancy
2.5kg
2.3kg
1.8kg
~90g/w
28w
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32w
birth
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Source:
http://images.tutorvista.com/cms/im
ages/38/molecular-orbital-theory.jpg
Smoke
• Contains many chemical agents
• We focus on: carbon monoxide CO
• colorless, tasteless gas, slightly less dense than air
• toxic to humans (in concentrations above about 35ppm)
• in smoke, reduces the oxygen supplied to the fetus
• A steady oxygen supply is critical for the developing baby
• Merkatz & Thompson (1990):
• smoking responsible for a 150-250 gram reduction in birth weight
• smoking mothers are twice as likely as nonsmoking mothers
to have a low-birth-weight baby (<2.5kg)
Source: http://pngimg.com/upload/smoke_PNG964.png
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Data: birth.txt
• Subset of CHDS: Child Health and Development Studies
• Pregnancies occurred between 1960-1967 in Oakland, CA
• birth.txt: data for 1236 babies
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Histograms
• histogram(data,nbins)creates a not normalized histogram
• histogram(data,nbins,’Normalization’,’pdf’)
creates a normalized (total area is 1) histogram of data
small babies
outliers
One mode, symmetric,
approximately bell-shaped
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One mode, not symmetric,
right-skewed
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Numerical Summaries
Location
• mean(x) returns the sample mean of x
• median(x) gives the median of x
• trimmean(x,200α) is the α-trimmed mean
Spread
• range(x) is range of x
• std(x,flag) is the standard deviation
• flag=0 ⇒
= 3.40
= 3.43
= 0.52
• flag=1 ⇒
• iqr(x) computes the interquartile range
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= 3.39
ACM 270-1, Lecture 2b: Dangers of Smoking
= 0.64
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Boxplot, Empirical CDF, QQ-plot
boxplot(x)
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ecdf(x)
ACM 270-1, Lecture 2b: Dangers of Smoking
qqplot(x)
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Smokers vs Nonsmokers
• Sample mean difference: ≈ 0.25 𝑘𝑘𝑘𝑘 (8.8 𝑜𝑜𝑜𝑜)
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