Homework 4

Due by 12/13/2015 ( Sunday! ).

Complete exercises and replicate outputs. Note that only PDF and HTML formats will be accepted. All R code you used to generate figures should be included in the document.

Word documents converted to PDF will no longer be accepted . Only documents with proper math typesetting ($\LaTeX$, $MathJax$, ...) are permitted. That means you either have to use $\LaTeX$ or one of knitr , sweave (part of RStudio) or jupyter .

If you decide to use pure $\LaTeX$ with listings package, you can use the following initialization code in the header

\usepackage{listings}
\lstset{language=R,
basicstyle=\footnotesize\ttfamily,
commentstyle=\ttfamily\color{gray},
numberstyle=\color{gray}\footnotesize,
numbers=left,
stepnumber=1,
frame=leftline,
breaklines=true}

and include blocks of code like this

\begin{lstlisting}[firstnumber=last]
...R-code...
\end{lstlisting}

If you are having troubles installing $\LaTeX$, you can use one of the online editors such as Overleaf or ShareLatex .

1. Moments of poisson distribution

Prove that both expected value and variance of random variable $X \sim Po(\lambda)$ is equal to $\lambda$.

Hint: use the fact that all probabilities sum to 1

2. Poisson distribution

Let $X$ be a number of deaths caused by horse kick in Prussian army forces (Bortkiewicz 1898) and let's assume it follows Poisson distribution with parameter $\lambda$, i.e. $X \sim Poiss(\lambda)$. We have data for 10 army units for 20 years with total sample size $M = 200$ ($200 = 10 \times 20$). Number of deaths in a single unit over one year is given in the following table, where $n$ is number of deaths and $m_n$ number of units with $n$ deaths. Calculate expected frequencies under the assumption that $X \sim Poiss(\lambda)$, where $\lambda = \frac{\sum_n n m_n}{\sum_n m_n}$.

$n$ 0 1 2 3 4 $\geq$ 5
$m_n$ 109 65 22 3 1 0

Display expected and observed frequencies in a table and calculate probability that there will be 4 or more deaths from theoretical model, i.e. $Pr(X \geq 4)$.

3. Finish exercise 25 (Normal distribution, simulation study I)

Don't forget to calculate $Pr(\bar{X}_n > 151)$ and make a comparison between theoretical probability and observed probability from simulated data.

4. Finish exercise 26 (Normal distribution, simulation study II)

Same as before, don't forget to compare theoretical probability with observed probability.