IT-223 - Assignment #2

Important: All questions in this assignment should be saved into a Microsoft Word document or any ‘doc’ or ‘RTF’ compatible file.  PDF is also fine. This file will then be submitted to COL. When using SPSS, note that you can right-click any graph and choose 'copy'. You can then paste the graph directly into your Word document.

Question #1 (8): Using a Normal probability table (a.k.a. z-table), find the percentage of observations from a standard Normal distribution that satisfies each of the following statements. 

a)    Z > 1.65

b)    Z < 1.65

c)    Z > -0.76

d)    -0.76 < Z < 1.65 

Question #2 (12): The ISTEP test is approximately Normally distributed with N(572, 51) i.e. mean of 572 and sd of 51.

  1. What score is needed in order to reach the 90th percentile or above?

  2. 75% of students will achieve a score of at least _____?

  3. What percentage of students will score between 400 and 600?

Question #3 (12): Use the file acidrain.sav found on the class web page. This dataset records the acidity of rainwater from a series of experiments. The acidity is recorded as 'pH' measurements. You will need to refer to the 'SPSS Primer' under 'Resources' to answer the problems for this question.

  1. Using SPSS, draw a histogram of the pH values from the experiments. Right click the graph, and paste it into your Word document. Do you think this data is normally distributed?

  2. Using SPSS, determine the mean and standard deviation of the pH. Look for 'Descriptive Statistics' in the SPSS Primer.

  3. A pH of 5 is quite acidic. What percentage of rainwater measurements had a pH below 5?

Question #4 (8): Use the file 'beer.sav'. This file gives, among other things, the carbohydrate content and calorie content for several different brands of beer. We'd like to determine whether or not the amount of carbohydrates is important in determining the caloric content of beer. (What do you think?).

  1. Use SPSS to generate a scatterplot, have it draw the regression line, and then determine 'r'. 

  2. Also note that there is an outlier (O'Doul's has 13.3 grams of carbs, but is only 70 calories). Enter the data window, and remove that value. Then redraw the scatterplot. What is the new value for 'r'? What is the term we use to describe a datapoint that has a significant effect on 'r'?

Again, submit your assignment to COL. As will always be the case, it is due 10 minutes before class time.