Why do we care whether the assumptions required

| April 14, 2018

Week 2: Understanding and Exploring AssumptionsYou will submit one Word document, including your SPSS output.1. Why do we care whether the assumptions required for statistical tests are met? (Tip: Youmight also want to write your answer on a note card you paste to your computer.)2. Open the data set that you corrected in Activity #1 for DownloadFestival.sav. You willuse the following variables: Day1, Day2, and Day3 (hygiene variable for all three days).Create a simple histogram for each variable. Choose to display the normal curve (underElement Properties) and title your charts. Copy these plots into your Word document.3. Now create probability-probability (p-p) plots for each variable. This output will give youadditional information. Read over the Case Processing Summary. Notice that there ismissing data for Days 2 and Day 3. Copy only the Normal p-p Plots into your Worddocument (you do not need to copy the beginning output nor the Detrended Normal p-pPlots).4. Examining the histograms and p-p plots, describe the dataset with particular attentiontoward the assumption of normality. For each day, do you think the responses arereasonably normally distributed? (Just give your impression of the data.) Why or whynot?5. Using the same dataset and the Frequency command, calculate the standard descriptivemeasures (mean, median, mode, standard deviation, variance and range) as well askurtosis and skew for all three hygiene variables. Paste your output into your Worddocument (you do not need to paste the Frequency Table). What does the output tell you?You will need to comment on: sample size, measures of central tendency and dispersionand well as kurtosis and skewness. You will need to either calculate z scores for skewnessand kurtosis or use those given in the book to provide a complete answer. Bottom line: isthe assumption of normality met for these three variables? Does this match your visualobservations from question #1?6. Using the dataset SPSSExam.sav and the Frequency command, calculate: the standarddescriptive statistics (mean, median, mode, standard deviation, variance and range) plusskew and kurtosis, and histograms with the normal curve on the following variables:Computer, Exam, Lecture, and Numeracy for the entire dataset. Complete the sameanalysis using University as a grouping variable. Paste your output into your Worddocument (you do not need to paste the Frequency Table). What do the results tell youwith regard to whether the data is normally distributed?7. Using the dataset SPSSExam.sav, determine whether the scores on computer literacy andpercentage of lectures attended (with University as a grouping variable) meet theassumption of homogeneity of variance (use Levene’s test). You must remember tounclick the “split file” option used above before conducting this test. What does theoutput tell you? (Be as specific as possible.)8. Describe the assumptions of normality and homogeneity of variance. When theseassumptions are violated, what are your options? Are there cases in which theassumptions may technically be violated, yet have no impact on your intended analyses?Explain.

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