Occurrences of Koalas in the Southern Tableland

Running head: OCCURRENCES OF KOALAS IN THE SOUTHERN TABLELAND
Occurrences of Koalas in the Southern Tableland
Name of Student
Name of University
Author Note

1OCCURRENCES OF KOALAS IN THE SOUTHERN TABLELAND
Table of Contents
Introduction......................................................................................................................................2
Statement of Hypothesis and Rationale of Method.........................................................................2
Analysis...........................................................................................................................................2
Conclusion.......................................................................................................................................7
Appendix..........................................................................................................................................8

2OCCURRENCES OF KOALAS IN THE SOUTHERN TABLELAND
Introduction
The paper is a study on the dataset Koala which documents observations concerning the
occurrences, that is, the presence or absence of koala bears over a number of sites spanning the
Southern Tablelands, located near, Cooma, NSW. It is to be determined whether elevation is a
good indicator of presence or absence of koala bears or not.
The data is based on the survey of 300 trees, where if some evidence of presence of koala
bears were found in the form of some tracks, faecal matter or the actual animal itself, was
marked as a site of presence (=1) otherwise it was marked as a site of absence (=0) and recorded
as the variable pa. The elevation of the site above sea level was also recorded as well as the
number of different species or diversity of trees in the individual site areas.
Statement of Hypothesis and Rationale of Method
The hypothesis under study is that elevation of a site has a significant effect on the
presence or absence of koala bears in that site. Defining the hypothesis in statistical terms, it can
be stated to be equivalent to the hypothesis that the coefficient of the variable elevation in the
logistic regression model of the variable pa.
The chosen model to fit the data is logistic regression with probit link. This was chosen
so, since the response variable, pa, takes binary values, 0 and 1. Therefore clearly the response
does not follow a normal distribution. The response considered in the probit model is the
conditional probability of response, pa, being 1 subject to a given elevation (Sperandei 2014).

3OCCURRENCES OF KOALAS IN THE SOUTHERN TABLELAND
Analysis
The analysis has been done using R.The following graph shows the distribution of the
recorded elevation (in metres) in the dataset.
Figure 1