stats
Psy 280 Spring 2019 Put your name on the back of the last page only.
Homework 10
1. A researcher is interested in finding out if there is an easier way to induce sleep at night. She designs a study with three groups of participants: One group puts on lavender lotion every night to induce sleepiness, a second group takes a melatonin pill before bed, and a third group is a control group who is not asked to try any sleep inducing method. After two weeks, the researcher asks participants in all three groups to rate their ease of being able to fall asleep (where higher numbers indicate more ease). The data for the three groups of people are displayed below.
Ease of Falling Asleep
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Control Group |
Lavender Lotion Group |
Melatonin Pill Group |
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6 |
8 |
9 |
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7 |
9 |
7 |
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10 |
10 |
8 |
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4 |
8 |
5 |
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5 |
6 |
6 |
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Mj |
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Nj |
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1. What are the dependent and independent variables (include levels of the independent variable)? 1 point
1. State the null and alternative hypothesis (symbols, not words). 1 point
1. Calculate the df-between, df-within, and find the critical value for this test at α = 0.05 1.5 points
1. Calculate the SS-between and the MS-between. 1.5 points
1. Calculate the SS-within, and the MS- within. 1.5 points
1. Calculate the obtained F. 1 point
1. Make a statistical decision about the null. Will you reject or retain the null based on your sample data? Why? 1 point
1. What do your results mean in words a layman would understand. 1/2 point
1. What information is missing for the interpretation of an ANOVA if you only run an omnibus/overall ANOVA (without any post-hoc tests)? Why do we need to run follow up tests when we conduct a One-Way ANOVA? 1 point
1. When we conduct a One-Way ANOVA, we first run an omnibus/overall test to see if a significant difference exists. If we obtain a significant F test statistic for the omnibus test, we move forward by conducting follow up tests. Why are follow-up tests done second as opposed to doing them first? 1 point
1. Compute the effect size, r2. Describe what r 2 means in the context of this research question. 1 point
1. Professor Housingpricesarekillingme is interested in finding out whether levels of housing satisfaction differ among students who live in houses, apartments, and dorms. Three groups of participants were identified for the study, including 10 students who live in houses near campus, 10 students who live in apartments near campus, and 10 students who live in the dorms. Each participant rated how satisfied they were with their current housing situation, where higher scores indicate greater levels of satisfaction.
Use SPSS to solve these problems. Open the ‘Homework 10 Dataset_S19.sav’ for this problem.
To conduct a one-way ANOVA in SPSS, Go to Analyze>General Linear Model>Univariate. Here plug in your “Dependent Variable” and put the IV in the “Fixed Factors” box. To get post-hoc tests, click the “Post-Hoc” button, click on your IV and then bring it over to the “Post-Hoc Tests for:” box by clicking the arrow. Click box below for appropriate post hoc test (LSD). In the “Options Menu” ask for “Descriptive Statistics” Hit Continue>OK to run the test.
1. Attach a copy of your output to the homework. (1/2 point)
1. What is the statistical result of the omnibus (overall) ANOVA? (Retain or reject the null and why [include F and p value]?) (1 point)
1. In the context of this study, what does the result of the omnibus test mean in words a layperson could understand? (1/2 point)
1. What are the statistical results for the three follow-up tests? Report the significance and whether you will reject or retain the null for each test. (3 points)
1. In the context of this study, what do the post-hoc results mean in words a layperson could understand? (1 point)
1. Compute r 2. (1/2 point)
1. What does r 2 mean in the context of this study? (1/2 point)