Download LAB 8 – BASIC DESCRIPTIVE STATISTICS

LAB 8 – BASIC DESCRIPTIVE STATISTICS
Purpose
The purpose of today’s lab is:
1. To help you solidify the conceptual meaning of two basic types of descriptive statistics – variability
and central tendency
2. To help you solidify the statistical basis of these concepts
3. To interpret them in a real research context
4. To work with SPSS and to discuss any problems that you encountered in the SPSS homework
assignment.
Preparation
1. Computation & Interpretation Assignments
a. Answer the following question:
Two classes of students took a test, with their scores listed below. Compute the mean and
variance for each of the data sets:
Class A: 50, 49, 51, 55, 45
Class B: 50, 40, 60, 80, 20
In statistical terms, describe the similarity and difference between the two data sets. Also, in plain
English, explain the difference between the two classes of students.
b. Pagano:
ch 4 – questions 13, 14, 15
c. Read the “Height and Weight” assignment and answer all of the questions.
2. SPSS Assignment
A researcher is interested in the association between conscientiousness and academic performance. She
recruits a small sample of participants (n=24), who completed the Brief Conscientiousness Scale (BCS)
and provided their overall GPA.
1) Enter their data (provided on the next page) into SPSS, being sure to name each of the variables, and
to provide a label for each. Recall that, we usually treat variables as the columns and participants (or
rats or whatever other units are measured) as the rows.
2) Have SPSS compute the total BCS score (the mean of the 3 items). Name this new variable
“BCStot,” and label it “BCS – Conscientiousness.” (Transform  Compute …..)
3) Be sure to save the data set to a folder on your computer where you’ll be able to find it later.
4) Compute the frequency tables and histograms for the two key variables – conscientiousness and gpa.
(Analyze  Descriptive Statistics  Frequencies ….)
5) Print out the data set and the SPSS output
6) Note the shape of the two distributions – is each one relatively normal (unskewed) or skewed? Just
make a note on the output.
Turn in the printed data set and output.
Raw data.
Note that you should enter each participant into a separate row, and each variable into a separate column. So
you should end up with a data set that has 24 rows and 4 columns (or 5, if you enter participant number as a
variable, which I generally do).
Partic.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
1
BCS Item
2
3
GPA
2
3
2
1
4
1
3
4
4
5
3
2
2
3
2
1
4
1
3
4
4
5
3
2
1
4
4
2
2
2
3
3
3
2
5
3
1
4
4
2
2
2
3
3
3
2
5
3
1.7
2
2.3
2.5
2.8
3
3.1
3.3
3.5
3.7
3.9
4
1.7
2
2.3
2.5
2.8
3
3.1
3.3
3.5
3.7
3.9
4
1
4
3
2
2
4
4
4
2
3
5
3
1
4
3
2
2
4
4
4
2
3
5
3
Partic.
1
BCS Item
2
3
GPA
Lab session
Question and answers about lecture
Turn in and discuss the computation and interpretation assignments
Turn in and discuss the SPSS assignment – discuss any difficulties
Use SPSS to run analysis of means, variances, etc for the data that you were working with during the
previous lab. (see the next page)
Lab 8 exercises - SPSS
Open the data file that we were working with last time (with SWL and STAI data).
Compute the sample mean and other descriptive statistics for the SWLTotal and the STAITotal
variables
1. Analyze  Desriptive Statistics  Descriptives
Compute the means etc separately for the two groups
1. Analyze  Compare means  Means
2. Put SWLTotal and STAITotal in the “Dependent List” box.
3. Put the Greek variable in the “Independent List” box.
4. Press the “Options” button and select the statistics that you want to examine for each group.
Highlight the statistic in the left box and press the arrow to move it into the right-hand side. At
least choose the number of cases, percent of total n, mean, median, variance, standard deviation,
and range.
5. Press the continue button, then press the OK button
Which group has the higher mean STAI score? If we know that two people are in different groups, what
would we guess about the relative size of their scores? What do we know about their scores?
Which group has the larger standard deviation – what does this tell us about the two groups?
Begin working with SPSS graphics capabilities Let’s compute a bar graph for group differences in
average SWL scores
1. Graphs  Bar.
2. Click “simple” and press the “Define” button.
3. Click the “Other summary function” choice.
4. Put SWLTotal in the “Variable” box.
5. Put the Greek variable in the “Category Axis” box.
6. Press the OK button.