# Prediction interval

windmill is used to generate direct current. Data are collected on a random sample of 45 different days

(over a period of 3 months) to determine the relationship between wind speed in mi/h and current in kA.

Researchers were interested in predicting current from wind speed. The data can be found in the file

windmill.sav.

a) Explore the relationship between wind speed and current. Include the following:

• A scatterplot with fitted regression line. (Graph should be edited appropriately).

• A description of the relationship in the sample (2-3 sentences)

• Testing of the least squares regression assumptions. (Graphs in this section do not need to be edited,

be careful to be specific about what you are seeing, don’t simply say for example linearity has been

met, describe what you are seeing and refer to the graph which leads you to this conclusion).

Remember graphs you directly refer to belong in the main body of the assignment next to where you

comment on them.

(8 marks)

b) Create the following two variables in SPSS, v?????????????????? and log10 ??????????????????. Explore the

relationship between current and v?????????????????? and also current and log10 ??????????????????. For each of

these relationships, you need to produce appropriate graphs and or statistics to see if all of the

assumptions of regression have been satisfied. Based upon how well the regression assumptions

have been met, decide which would be the better choice.

(10 marks)

c) Use the best model found in part b to:

I. write the least squares regression equation in terms of the variables

II. interpret the slope

III. to predict the current when wind speed is 5.0mi/h.

(4 marks)

d) Using the best model found in part b, find and interpret a 95% prediction interval for the current on a

given day when the wind speed is 5.0mi/h, include a screenshot from SPSS showing where you

obtained the prediction interval.