ENVX3002: Statistics in the Natural Sciences

Assessment 1

submission. WEIGHTING: 12.5%, mark is out of 20

1. The assessable exercises you submit must be your own work

2. All answers are to be submitted via Turnitin as a HTML, PDF, or Word file.

3. Combined answers should not be longer than 6 pages.

4. Marks will be deducted for sloppy presentation.

5. Include your R code either in situ in the document with rmarkdown, or as an

Appendix

An experiment was performed to understand how the width of the stems of birch trees (cm)

varies under different growing conditions. The aim is to find the conditions which maximise

the width of the stems. The conditions were (i) planting density (no. plants/m2

); 1, 2 and 5

(ii) type of mulch; no mulch, bark mulch, plastic mulch (iii) levels of irrigation in % of field

capacity; 0, 33, 66, 100. The researchers had complete control over the experiment.

The data is provided below, and in the Excel file birch.xlsx. It will need to be suitably

rearranged to facilitate analysis.

No Mulch Bark Mulch Plastic Mulch

Plant

Density

Irrigation (% FC)

0 33 66 100 0 33 66 100 0 33 66 100

1 15 16 21 21 18 18 23 21 20 19 20 21

1 13 20 19 19 17 20 26 18 16 23 22 18

1 17 19 23 14 18 27 27 16 16 26 25 9

1 11 15 22 17 12 15 24 17 14 19 16 17

1 12 21 26 18 20 24 28 20 22 20 25 18

2 16 18 22 24 15 20 25 22 15 23 18 18

2 19 20 26 18 22 23 26 15 22 18 21 14

2 12 21 20 18 14 27 19 13 18 27 23 13

2 14 21 21 22 15 24 27 20 19 26 20 20

2 14 21 18 17 13 21 20 16 24 26 19 15

5 10 13 16 15 10 17 19 14 11 19 16 14

5 9 10 19 15 14 17 27 16 20 17 22 18

5 13 14 20 15 23 24 24 12 22 20 21 11

5 10 11 23 22 18 15 28 12 21 17 16 10

5 9 15 16 16 18 16 22 12 23 17 20 12

You are required to analyse the experiment and prepare your analysis in a report.

Your report should include amongst other things

(i) a specification of the experimental design, explaining your reasoning;

(ii) a specification of the model being fitted, including any model assumptions

(iii) an assessment of the fit of the model

(iv) statistical and biological conclusions from your analysis, indicating specific

outcomes from your analysis pertinent to maximising the width of birch tree

stems.