Added to statistical inference section with scipy: hypothesis testing…

… notebook.

scipy/first.py

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+"""This file contains code used in "Think Stats",
+by Allen B. Downey, available from greenteapress.com
+
+Copyright 2014 Allen B. Downey
+License: GNU GPLv3 http://www.gnu.org/licenses/gpl.html
+"""
+
+from __future__ import print_function
+
+import math
+import numpy as np
+
+import nsfg
+import thinkstats2
+import thinkplot
+
+
+def MakeFrames():
+    """Reads pregnancy data and partitions first babies and others.
+
+    returns: DataFrames (all live births, first babies, others)
+    """
+    preg = nsfg.ReadFemPreg()
+
+    live = preg[preg.outcome == 1]
+    firsts = live[live.birthord == 1]
+    others = live[live.birthord != 1]
+
+    assert len(live) == 9148
+    assert len(firsts) == 4413
+    assert len(others) == 4735
+
+    return live, firsts, others
+
+
+def Summarize(live, firsts, others):
+    """Print various summary statistics."""
+
+    mean = live.prglngth.mean()
+    var = live.prglngth.var()
+    std = live.prglngth.std()
+
+    print('Live mean', mean)
+    print('Live variance', var)
+    print('Live std', std)
+
+    mean1 = firsts.prglngth.mean()
+    mean2 = others.prglngth.mean()
+
+    var1 = firsts.prglngth.var()
+    var2 = others.prglngth.var()
+
+    print('Mean')
+    print('First babies', mean1)
+    print('Others', mean2)
+
+    print('Variance')
+    print('First babies', var1)
+    print('Others', var2)
+
+    print('Difference in weeks', mean1 - mean2)
+    print('Difference in hours', (mean1 - mean2) * 7 * 24)
+
+    print('Difference relative to 39 weeks', (mean1 - mean2) / 39 * 100)
+
+    d = thinkstats2.CohenEffectSize(firsts.prglngth, others.prglngth)
+    print('Cohen d', d)
+
+
+def PrintExtremes(live):
+    """Plots the histogram of pregnancy lengths and prints the extremes.
+
+    live: DataFrame of live births
+    """
+    hist = thinkstats2.Hist(live.prglngth)
+    thinkplot.Hist(hist, label='live births')
+
+    thinkplot.Save(root='first_nsfg_hist_live', 
+                   title='Histogram',
+                   xlabel='weeks',
+                   ylabel='frequency')
+
+    print('Shortest lengths:')
+    for weeks, freq in hist.Smallest(10):
+        print(weeks, freq)
+
+    print('Longest lengths:')
+    for weeks, freq in hist.Largest(10):
+        print(weeks, freq)
+
+
+def MakeHists(live):
+    """Plot Hists for live births
+
+    live: DataFrame
+    others: DataFrame
+    """
+    hist = thinkstats2.Hist(live.birthwgt_lb, label='birthwgt_lb')
+    thinkplot.Hist(hist)
+    thinkplot.Save(root='first_wgt_lb_hist', 
+                   xlabel='pounds',
+                   ylabel='frequency',
+                   axis=[-1, 14, 0, 3200])
+
+    hist = thinkstats2.Hist(live.birthwgt_oz, label='birthwgt_oz')
+    thinkplot.Hist(hist)
+    thinkplot.Save(root='first_wgt_oz_hist', 
+                   xlabel='ounces',
+                   ylabel='frequency',
+                   axis=[-1, 16, 0, 1200])
+
+    hist = thinkstats2.Hist(np.floor(live.agepreg), label='agepreg')
+    thinkplot.Hist(hist)
+    thinkplot.Save(root='first_agepreg_hist', 
+                   xlabel='years',
+                   ylabel='frequency')
+
+    hist = thinkstats2.Hist(live.prglngth, label='prglngth')
+    thinkplot.Hist(hist)
+    thinkplot.Save(root='first_prglngth_hist', 
+                   xlabel='weeks',
+                   ylabel='frequency',
+                   axis=[-1, 53, 0, 5000])
+
+
+def MakeComparison(firsts, others):
+    """Plots histograms of pregnancy length for first babies and others.
+
+    firsts: DataFrame
+    others: DataFrame
+    """
+    first_hist = thinkstats2.Hist(firsts.prglngth, label='first')
+    other_hist = thinkstats2.Hist(others.prglngth, label='other')
+
+    width = 0.45
+    thinkplot.PrePlot(2)
+    thinkplot.Hist(first_hist, align='right', width=width)
+    thinkplot.Hist(other_hist, align='left', width=width)
+
+    thinkplot.Save(root='first_nsfg_hist', 
+                   title='Histogram',
+                   xlabel='weeks',
+                   ylabel='frequency',
+                   axis=[27, 46, 0, 2700])
+
+
+def main(script):
+    live, firsts, others = MakeFrames()
+
+    MakeHists(live)
+    PrintExtremes(live)
+    MakeComparison(firsts, others)
+    Summarize(live, firsts, others)
+
+
+if __name__ == '__main__':
+    import sys
+    main(*sys.argv)
+
+