chap02ex02soln.ipynb

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   "source": [
    "# Exercise 2.2: Solution"
   ]
  },
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "The <b>mode</b> of a distribution is the most frequent value.\n",
    "\n",
    "Write a function called Mode that takes a Hist and returns the most frequent value. "
   ]
  },
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   "cell_type": "code",
   "execution_count": 1,
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   "source": [
    "def Mode(hist):\n",
    "    p, x = max([(p, x) for x, p in hist.Items()])\n",
    "    return x"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Write a function called AllModes that returns a list of value-frequency pairs in descending order of frequency. "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "from operator import itemgetter\n",
    "\n",
    "def AllModes(hist):\n",
    "    return sorted(hist.Items(), key=itemgetter(1), reverse=True)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Using the variable totalwgt_lb, investigate whether first babies are lighter or heavier than others. "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "preg.totalwgt_lb"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
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   "outputs": [],
   "source": [
    "first_babies.totalwgt_lb.mean()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "other_babies.totalwgt_lb.mean()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "The result is -0.088672927072602. It is negative since the first group is larger than the other. It is still small. "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Compute Cohen’s d to quantify the difference between the groups. How does it compare to the difference in pregnancy length?"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "# first babies\n",
    "group1_lb = first_babies.totalwgt_lb\n",
    "# other babies\n",
    "group2_lb = other_babies.totalwgt_lb\n",
    "CohenEffectSize(group1_lb, group2_lb)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "The result is bigger than the differences in pregnancy lengths, but still small. "
   ]
  }
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