From: Andrew Lorimer <andrew@lorimer.id.au>
Date: Thu, 25 Jul 2019 00:06:41 +0000 (+1000)
Subject: [methods] probability distributions
X-Git-Tag: yr12~83
X-Git-Url: https://git.lorimer.id.au/notes.git/diff_plain/8057d3199209e2598717ce825c6523c5df9981c8?hp=528685ecf6d6c1ded844627528f3ff232c073d8b

[methods] probability distributions
---

diff --git a/methods/statistics.pdf b/methods/statistics.pdf
index 8fb6a89..b0114ea 100644
Binary files a/methods/statistics.pdf and b/methods/statistics.pdf differ
diff --git a/methods/statistics.tex b/methods/statistics.tex
index 590e547..04a1903 100644
--- a/methods/statistics.tex
+++ b/methods/statistics.tex
@@ -20,18 +20,40 @@
   \date{}
   \maketitle
 
+  \section{Probability}
+
+  \[ \Pr(A \cup B) = \Pr(A) + \Pr(B) - \Pr(A \cap B) \]
+  \[ \Pr(A \cup B) = 0 \tag{mutually exclusive} \]
+
   \section{Conditional probability}
 
   \[ \Pr(A|B) = \frac{\Pr(A \cap B)}{\Pr(B)} \quad \text{where } \Pr(B) \ne 0 \]
   
   \[ \Pr(A) = \Pr(A|B) \cdot \Pr(B) + \Pr(A|B^{\prime}) \cdot \Pr(B^{\prime}) \tag{law of total probability} \]
+  
+  \[ \Pr(A \cap B) = \Pr(A|B) \times \Pr(B) \tag{multiplication theorem} \]
 
   For independent events:
   
   \begin{itemize}
-    \item \(\Pr(A \cap B) = \Pr(A) \cdot \Pr(B)\)
+    \item \(\Pr(A \cap B) = \Pr(A) \times \Pr(B)\)
     \item \(\Pr(A|B) = \Pr(A)\)
     \item \(\Pr(B|A) = \Pr(B)\)
   \end{itemize}
 
+  \subsection{Discrete random distributions}
+
+  Any experiment or activity involving chance will have a probability associated with each result or \textit{outcome}. If the outcomes have a reference to \textbf{discrete numeric values} (outcomes that can be counted), and the result is unknown, then the activity is a \textit{discrete random probability distribution}.
+
+  \subsubsection{Discrete probability distributions}
+  
+  If an activity has outcomes whose probability values are all positive and less than one ($\implies 0 \le p(x) \le 1$), and for which the sum of all outcome probabilities is unity ($\implies \sum p(x) = 1$), then it is called a \textit{probability distribution} or \textit{probability mass} function.
+
+  \begin{itemize}
+    \item \textbf{Probability distribution graph} - a series of points on a cartesian axis representing results of outcomes. $\Pr(X=x)$ is on $y$-axis, $x$ is on $x$ axis.
+    \item \textbf{Mean $\mu$} - measure of central tendency. \textit{Balance point} or \textit{expected value} of a distribution. Centre of a symmetrical distribution.
+    \item \textbf{Variance $\sigma^2$} - measure of spread of data around the mean. Not the same magnitude as the original data. Represented by $\sigma^2=\operatorname{Var}(x) = \sum (x=\mu)^2 \times p(x) = \sum (x-\mu)^2 \times \Pr(X=x)$. Alternatively: $\sigma^2 = \operatorname{Var}(X) = \sum x^2 \times p(x) - \mu^2$
+    \item \textbf{Standard deviation $\sigma$} - measure of spread in the original magnitude of the data. Found by taking square root of the variance: $\sigma =\operatorname{sd}(X)=\sqrt{\operatorname{Var}(X)}$
+  \end{itemize}
+
 \end{document}