Study questions

1. Define the term 'contrast'. Describe the circumstances when a contrast can be useful in an analysis of variance.
2. Plants were randomly selected for the recording of plant height and leaf number when only a proportion of plants had emerged. Think of an alternative method that might reduce possible bias and provide a more accurate estimate of average plant height across the whole plot.

3. Use the Spread → Restrict/Filter command in GenStat to select data for plant height in CS15Data1 for each week in turn. Analyse each week separately using the design for a randomised block and comment on the changes in residual variance. Explain how you feel statistical analysis should proceed and give your reasons.
4. Again using the data for plant height calculate linear and quadratic contrasts for week. To do this calculate the linear transformation (-3xweek1 -1xweek2 +1xweek3 +3xweek4) and the quadratic transformation (-1xweek1 +1xweek2 +1xweek3 -1xweek4). Note that in order to do this calculation you will first need to unstack the data. Perform an analysis of variance of these two variables and comment on the results of the analysis.
5. Repeat Question 3 using number of leaves instead of plant height.
6. Repeat Question 4 using number of leaves instead of plant height.