-\documentclass[a4paper]{article}
-\usepackage[a4paper, margin=2cm]{geometry}
-\usepackage{array}
-\usepackage{amsmath}
-\usepackage{amssymb}
-\usepackage{tcolorbox}
-\usepackage{fancyhdr}
-\usepackage{pgfplots}
-\usepackage{tabularx}
-\usepackage{keystroke}
-\usepackage{listings}
-\usepackage{xcolor} % used only to show the phantomed stuff
-\definecolor{cas}{HTML}{e6f0fe}
-\usepackage{mathtools}
-\pgfplotsset{compat=1.16}
-
-\pagestyle{fancy}
-\fancyhead[LO,LE]{Unit 4 Specialist --- Statistics}
-\fancyhead[CO,CE]{Andrew Lorimer}
-
-\setlength\parindent{0pt}
-
+\documentclass[spec-collated.tex]{subfiles}
\begin{document}
- \title{Statistics}
- \author{}
- \date{}
- \maketitle
-
- \section{Linear combinations of random variables}
+ \section{Statistics}
\subsection*{Continuous random variables}
\item \(\int^\infty_{-\infty} f(x) \> dx = 1\)
\end{enumerate}
+ \begin{align*}
+ E(X) &= \int_\textbf{X} (x \cdot f(x)) \> dx \\
+ \operatorname{Var}(X) &= E\left[(X-\mu)^2\right]
+ \end{align*}
+
\[ \Pr(X \le c) = \int^c_{-\infty} f(x) \> dx \]
+
- \subsubsection*{Linear functions \(X \rightarrow aX+b\)}
+ \subsection*{Two random variables \(X, Y\)}
+
+ If \(X\) and \(Y\) are independent:
+ \begin{align*}
+ \operatorname{E}(aX+bY) & = a\operatorname{E}(X)+b\operatorname{E}(Y) \\
+ \operatorname{Var}(aX \pm bY \pm c) &= a^2 \operatorname{Var}(X) + b^2 \operatorname{Var}(Y)
+ \end{align*}
+
+ \subsection*{Linear functions \(X \rightarrow aX+b\)}
\begin{align*}
\Pr(Y \le y) &= \Pr(aX+b \le y) \\
\textbf{Variance:} && \operatorname{Var}(aX+b) &= a^2 \operatorname{Var}(X) \\
\end{align*}
- \subsection*{Linear combination of two random variables}
+ \subsection*{Expectation theorems}
+
+ For some non-linear function \(g\), the expected value \(E(g(X))\) is not equal to \(g(E(X))\).
\begin{align*}
- \textbf{Mean:} && \operatorname{E}(aX+bY) & = a\operatorname{E}(X)+b\operatorname{E}(Y) \\
- \textbf{Variance:} && \operatorname{Var}(aX+bY) &= a^2 \operatorname{Var}(X) + b^2 \operatorname{Var}(Y) \tag{if \(X\) and \(Y\) are independent}\\
+ E(X^2) &= \operatorname{Var}(X) - \left[E(X)\right]^2 \\
+ E(X^n) &= \Sigma x^n \cdot p(x) \tag{non-linear} \\
+ &\ne [E(X)]^n \\
+ E(aX \pm b) &= aE(X) \pm b \tag{linear} \\
+ E(b) &= b \tag{\(\forall b \in \mathbb{R}\)}\\
+ E(X+Y) &= E(X) + E(Y) \tag{two variables}
\end{align*}
- \section{Sample mean}
+ \subsection*{Sample mean}
Approximation of the \textbf{population mean} determined experimentally.
\[ \overline{x} = \dfrac{\Sigma x}{n} \]
- where \(n\) is the size of the sample (number of sample points) and \(x\) is the value of a sample point
-
- \begin{tcolorbox}[colframe=cas!75!black, title=On CAS]
+ where
+ \begin{description}[nosep, labelindent=0.5cm]
+ \item \(n\) is the size of the sample (number of sample points)
+ \item \(x\) is the value of a sample point
+ \end{description}
- \begin{enumerate}
+\begin{cas}
+ \begin{enumerate}[leftmargin=3mm]
\item Spreadsheet
- \item In cell A1: \verb;mean(randNorm(sd, mean, sample size));
+ \item In cell A1:\\ \path{mean(randNorm(sd, mean, sample size))}
\item Edit \(\rightarrow\) Fill \(\rightarrow\) Fill Range
\item Input range as A1:An where \(n\) is the number of samples
\item Graph \(\rightarrow\) Histogram
\end{enumerate}
- \end{tcolorbox}
+ \end{cas}
\subsubsection*{Sample size of \(n\)}
For a new distribution with mean of \(n\) trials, \(\operatorname{E}(X^\prime) = \operatorname{E}(X), \quad \operatorname{sd}(X^\prime) = \dfrac{\operatorname{sd}(X)}{\sqrt{n}}\)
- \begin{tcolorbox}[colframe=cas!75!black, title=On CAS]
+ \begin{cas}
\begin{itemize}
\item Spreadsheet \(\rightarrow\) Catalog \(\rightarrow\) \verb;randNorm(sd, mean, n); where \verb;n; is the number of samples. Show histogram with Histogram key in top left
\item To calculate parameters of a dataset: Calc \(\rightarrow\) One-variable
\end{itemize}
- \end{tcolorbox}
+
+ \end{cas}
- \section{Normal distributions}
+ \subsection*{Normal distributions}
- mean = mode = median
\[ Z = \frac{X - \mu}{\sigma} \]
- Normal distributions must have area (total prob.) of 1 \(\implies \int^\infty_{-\infty} f(x) \> dx = 1\)
+ Normal distributions must have area (total prob.) of 1 \(\implies \int^\infty_{-\infty} f(x) \> dx = 1\) \\
+ \(\text{mean} = \text{mode} = \text{median}\)
+
+ \begin{warning}
+ Always express \(z\) as +ve. Express confidence \textit{interval} as ordered pair.
+ \end{warning}
+
\pgfmathdeclarefunction{gauss}{2}{%
\pgfmathparse{1/(#2*sqrt(2*pi))*exp(-((x-#1)^2)/(2*#2^2))}%
}
-
-{\begin{center} \begin{tikzpicture}
- \pgfplotsset{set layers}
+ \pgfplotsset{every axis/.append style={
+ axis x line=middle, % put the x axis in the middle
+ axis y line=middle, % put the y axis in the middle
+ }} \pgfkeys{/pgf/decoration/.cd,
+ distance/.initial=10pt
+} \pgfdeclaredecoration{add dim}{final}{
+\state{final}{%
+\pgfmathsetmacro{\dist}{5pt*\pgfkeysvalueof{/pgf/decoration/distance}/abs(\pgfkeysvalueof{/pgf/decoration/distance})}
+ \pgfpathmoveto{\pgfpoint{0pt}{0pt}}
+ \pgfpathlineto{\pgfpoint{0pt}{2*\dist}}
+ \pgfpathmoveto{\pgfpoint{\pgfdecoratedpathlength}{0pt}}
+ \pgfpathlineto{\pgfpoint{(\pgfdecoratedpathlength}{2*\dist}}
+ \pgfsetarrowsstart{latex}
+ \pgfsetarrowsend{latex}
+ \pgfpathmoveto{\pgfpoint{0pt}{\dist}}
+ \pgfpathlineto{\pgfpoint{\pgfdecoratedpathlength}{\dist}}
+ \pgfusepath{stroke}
+ \pgfpathmoveto{\pgfpoint{0pt}{0pt}}
+ \pgfpathlineto{\pgfpoint{\pgfdecoratedpathlength}{0pt}}
+}}
+\tikzset{dim/.style args={#1,#2}{decoration={add dim,distance=#2},
+ decorate,
+ postaction={decorate,decoration={text along path,
+ raise=#2,
+ text align={align=center},
+ text={#1}}}}}
+ \begin{figure*}[hb]
+ \centering
+ {\begin{center} \begin{tikzpicture}
+ \pgfplotsset{set layers, axis x line=middle, axis y line=middle}
\begin{axis}[every axis plot post/.append style={
mark=none,domain=-3:3,samples=50,smooth},
axis x line=bottom,
every axis y label/.style={at={(axis description cs:-0.02,0.2)}, anchor=south west, rotate=90},
ylabel={\(\Pr(X=x)\)}]
\addplot {gauss(0,0.75)};
+\fill[red!30] (-3,0) -- plot[id=f3,domain=-3:3,samples=50]
+ function {1/(0.75*sqrt(2*pi))*exp(-((x)^2)/(2*0.75^2))} -- (3,0) -- cycle;
+ \fill[darkgray!30] (3,0) -- plot[id=f3,domain=-3:3,samples=50] function {1/(0.75*sqrt(2*pi))*exp(-x*x*0.5/(0.75*0.75))} -- (3,0) -- cycle;
+ \fill[lightgray!30] (-2,0) -- plot[id=f3,domain=-2:2,samples=50] function {1/(0.75*sqrt(2*pi))*exp(-x*x*0.5/(0.75*0.75))} -- (2,0) -- cycle;
+ \fill[white!30] (-1,0) -- plot[id=f3,domain=-1:1,samples=50] function {1/(0.75*sqrt(2*pi))*exp(-x*x*0.5/(0.75*0.75))} -- (1,0) -- cycle;
+ \begin{scope}[<->]
+ \draw (-1,0.35) -- (1,0.35) node [midway, fill=white] {68.3\%};
+ \draw (-2,0.25) -- (2,0.25) node [midway, fill=white] {95.5\%};
+ \draw (-3,0.15) -- (3,0.15) node [midway, fill=white] {99.7\%};
+ \end{scope}
+ \begin{scope}[-, dashed, gray]
+ \draw (-1,0) -- (-1, 0.35);
+ \draw (1,0) -- (1, 0.35);
+ \draw (-2,0) -- (-2, 0.25);
+ \draw (2,0) -- (2, 0.25);
+ \draw (-3,0) -- (-3, 0.15);
+ \draw (3,0) -- (3, 0.15);
+ \end{scope}
\end{axis}
\begin{axis}[every axis plot post/.append style={
mark=none,domain=-3:3,samples=50,smooth},
\addplot {gauss(0,0.75)};
\end{axis}
\end{tikzpicture}\end{center}}
+ \end{figure*}
- \section{Central limit theorem}
+ \subsection*{Central limit theorem}
If \(X\) is randomly distributed with mean \(\mu\) and sd \(\sigma\), then with an adequate sample size \(n\) the distribution of the sample mean \(\overline{X}\) is approximately normal with mean \(E(\overline{X})\) and \(\operatorname{sd}(\overline{X}) = \frac{\sigma}{\sqrt{n}}\).
+ \subsection*{Confidence intervals}
+
+ \begin{itemize}
+ \item \textbf{Point estimate:} single-valued estimate of the population mean from the value of the sample mean \(\overline{x}\)
+ \item \textbf{Interval estimate:} confidence interval for population mean \(\mu\)
+ \item \(C\)\% confidence interval \(\implies\) \(C\)\% of samples will contain population mean \(\mu\)
+ \end{itemize}
+
+ \subsubsection*{95\% confidence interval}
+
+ For 95\% c.i. of population mean \(\mu\):
+
+ \[ x \in \left(\overline{x} \pm 1.96 \dfrac{\sigma}{\sqrt{n}} \right)\]
+
+ where:
+ \begin{description}[nosep, labelindent=0.5cm]
+ \item \(\overline{x}\) is the sample mean
+ \item \(\sigma\) is the population sd
+ \item \(n\) is the sample size from which \(\overline{x}\) was calculated
+ \end{description}
+
+ \begin{cas}
+ Menu \(\rightarrow\) Stats \(\rightarrow\) Calc \(\rightarrow\) Interval \\
+ Set \textit{Type = One-Sample Z Int} \\ \-\hspace{1em} and select \textit{Variable}
+ \end{cas}
+
+ \subsection*{Margin of error}
+
+ For 95\% confidence interval of \(\mu\):
+ \begin{align*}
+ M &= 1.96 \times \dfrac{\sigma}{\sqrt{n}} \\
+ \implies n &= \left( \dfrac{1.96 \sigma}{M} \right)^2
+ \end{align*}
+
+ Always round \(n\) up to a whole number of samples.
+
+ \subsection*{General case}
+
+ For \(C\)\% c.i. of population mean \(\mu\):
+
+ \[ x \in \left( \overline{x} \pm k \dfrac{\sigma}{\sqrt{n}} \right) \]
+ \hfill where \(k\) is such that \(\Pr(-k < Z < k) = \frac{C}{100}\)
+
+ \subsection*{Confidence interval for multiple trials}
+
+ For a set of \(n\) confidence intervals (samples), there is \(0.95^n\) chance that all \(n\) intervals contain the population mean \(\mu\).
+
+ \section{Hypothesis testing}
+
+ \begin{warning}
+ Note hypotheses are always expressed in terms of population parameters
+ \end{warning}
+
+ \subsection*{Null hypothesis \(H_0\)}
+
+ Sample drawn from population has same mean as control population, and any difference can be explained by sample variations.
+
+ \subsection*{Alternative hypothesis \(H_1\)}
+
+ Amount of variation from control is significant, despite standard sample variations.
+
+ \subsection*{\(p\)-value}
+
+ Probability of observing a value of the sample statistic as significant as the one observed, assuming null hypothesis is true.
+
+ % table of p-values for strength of evidence
+
+ \subsection*{Distribution of sample mean}
+
+ If \(X \sim \operatorname{N}(\mu, \sigma)\), then distribution of sample mean \(\overline{X}\) is also normal with \(\overline{X} \sim \operatorname{N}(\mu, \frac{\sigma}{\sqrt{n}}\).
+
+ \subsection*{Statistical significance}
+
+ Significance level is denoted by \(\alpha\).
+
+ \-\hspace{1em} If \(p<\alpha\), null hypothesis is \textbf{rejected} \\
+ \-\hspace{1em} If \(p>\alpha\), null hypothesis is \textbf{accepted}
+
+ \subsection*{\(z\)-test}
+
+ Hypothesis test for a mean of a sample drawn from a normally distributed population with a known standard deviation.
+
+ \begin{cas}
+ Menu \(\rightarrow\) Statistics \(\rightarrow\) Calc \(\rightarrow\) Test. \\
+ Select \textit{One-Sample Z-Test} and \textit{Variable}, then input:
+ \begin{description}[nosep, style=multiline, labelindent=0.5cm, leftmargin=2cm, font=\normalfont]
+ \item[\(\mu\) cond:] same operator as \(H_1\)
+ \item[\(\mu_0\):] expected sample mean (null hypothesis)
+ \item[\(\sigma\):] standard deviation (null hypothesis)
+ \item[\(\overline{x}\):] sample mean
+ \item[\(n\):] sample size
+ \end{description}
+ \end{cas}
+
\end{document}