Biostatistics Practical Exam
13/03/2018
Write the answers to all questions (R code + your comments) in an R script called
Exam_####.R
(replace #### for your name and surname) and submit it to the virtual campus.
Exercise 1 (10 pts)
To investigate the effects of habitat fragmentation, researchers related the abundance of forest birds to a
range of variables (including patch area, number of years of isolation, distance to the nearest patch and
larger patch, grazing intensity and altitude) collected from a total of 56 forest patches. Data are reported in
“loyn.csv”.
1- AREA, DIST and LDIST variables are non-normal, apply a log10 transformation on these variables. (2
pts)
2- Apply pairwise correlations for the variables ALT, GRAZE and YR.ISOL. State the result of your analysis.
(3 pts)
3- Apply a single analysis to study the abundance of forest birds en function of all explanatory variables.
State the result of your analysis. (5 pts)
Exercise 2 (10 pts)
Researchers investigated the density of adult limpets (6, 12 and 24 individuals per enclosure) during two
seasons (winter-spring and summer-autumn) so as to investigate their effects on egg mass production. Three
replicate enclosures per density/season combination were used. Data are reported in “quinn.txt”.
1- Analyse the whole data set and report the result. (5 pts)
2- Report the interaction plot. Explain the result. (2 pts)
3- Perform the pairwise comparison test when appropriate and report the result. (3 pts)
Exercise 3 (10 pts)
Two analysts, A and B each prepared five replicate samples to measure the pH of a specific sample of soil.
Results are the following:
A B
8.208 8.389
8.239 8.393
8.258 8.399
8.264 8.413
8.283 8.423
1- First create a dataframe of the data within R. (1 pts)
2- Report the mean and the variance for A and B. (1 pts)
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