An experimental design problem is detailed below. A series of questions follow the problem statement. Use SPSS to obtain appropriate analyses of the data where required and use the SPSS output obtained in answering the questions that follow the problem statement. You must copy sections of your SPSS output into this document where requested.
Carry out an appropriate parametric test to detect whether or not there is a significant difference in average seedling height between mean daily watering and weekly watering. State your hypotheses, test statistics and conclusion (you may assume equal variances in answering this question).
(4 marks)
State what type of experimental design model you would use to investigate simultaneously, the influence of both factors ‘watering’ and ‘sunlight’ on growth (measured by height). Give the (generic) model and explain all of the terms in your model.
(4 marks)
Use SPSS to run your chosen model for the outcome variable ‘growth’ (as measured by height). Use the SPSS output to complete the ANOVA table below. (alternatively, you may copy and paste the appropriate table from SPSS output and highlight the relevant content)
SS (sum of squares) Df Mean Square F
Factor A
Factor B
Factor A*B
Error
Total
(9 marks)
Using a 5% significance level carry out F tests to investigate differences in average results between the main effects for factors watering and sunlight and their interaction separately. (You should define factors A and B, and clearly state your hypotheses, test statistics and conclusions, use α=0.05)
(12 marks)
Use SPSS to perform an appropriate post hoc test to examine differences between subgroups of the factor warmup. Copy and paste the relevant SPSS output here. Use the output obtained to identify any differences that exist and describe the nature of any such differences in the context of the experiment,
(6 marks)
State your final model for this experiment and obtain estimated parameter values for the model. Copy and paste the relevant SPSS output here. Explain what the estimated parameter values mean in the context of the model.
(10 marks)
Use this model to calculate the predicted growth at the end of the two month experiment when daily watering and a moderate exposure to sunlight are combined.
(2 marks)
What would the difference in average growth be if the watering regime was changed to weekly?
(3 marks)