MATH363: EXAMPLE question for Final Assessment
This is an EXAMPLE of a question that is SIMILAR in STYLE to the final assessment. The ques-
tions in final assessment will not be the same as this one but of similar level of difficulty.
The yield of potato is believed to depend on the soil pH and soil salinity. An experiment was designed to
investigate how these explanatory variables affect the yield: for each plot of land the average yield per plant (yi)
as well as soil pH and soil salinity were recorded. The varieties are coded as 1–Abbot, 2–Cara, 3–Mira. The data
are in the file potato.sav.
(a) Obtain scatter plots of the data and suggest a possible model. Fit that model and provide practical
interpretation.
[Marks 30]
(b) Decide if the model fits well. You need to include residual analysis in this section.
[Marks 20]
(c) You are also asked to fit separate coefficients for the different varieties. Write down the model equation
for such a model, fit it using SPSS and comment on your results.
[Marks 30]
(d) The researchers want to use the model to obtain prediction of yield for Setanta variety from a plot with
pH 3 and salinity 12. What would you tell the researchers and what values would you give them to answer
their question?
[Marks 20]
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