Chapter 1

Displaying the Order in a Group of Numbers

and…Intro to SPSS (Activity 1)

Thurs. Aug 22, 2013

The Two Branches of Statistical Methods

Descriptive statistics– Summarize/organize

• Inferential statistics– Draw conclusions/make inferences

Basic Concepts

Variable– A condition or characteristic that can have different values

– Example?

Value– A possible number or category that a score can have

– Example?

Score– A particular person’s value on a variable

Levels of Measurement Numeric (quantitative) variable

– Equal-interval variablesExample?

– Rank-order (ordinal) variables• Example?

Nominal (categorical) variables– Example?

Frequency Tables

Provide a listing of individuals having each of the different values for a particular variable.

e.g., stress ratings of 151 students: 4,7,7,7,8,8,7,8,9,4,7,3,6,9,10,5,7,10,6,8,7,8,7,8,7,4,5,10,10,0,9,8,3,7,9,7,9,5,8,5,0,4,6,6,7,5,3,2,8,5,10,9,10,6,4,8,8,8,4,8,7,3,8,8,8,8,7,9,7,5,6,3,4,8,7,5,7,3,3,6,5,7,5,7,8,8,7,10,5,4,3,7,6,3,9,7,8,5,7,9,9,3,1,8,6,6,4,8,5,10,4,8,10,5,5,4,9,4,7,7,7,6,6,4,4,4,9,7,10,4,7,5,10,7,9,2,7,5,9,10,3,7,2,5,9,8,10,10,6,8,3

Steps for Making a Frequency Table

• Make a list down the page of each possible value, from highest to lowest

• Go one by one through the scores, making a mark for each next to its value on the list

• Make a table showing how many times each value on your list is used

• Figure the percentage of scores for each value

A Frequency Table:

Stress Rating

Frequency

Percent

10 14 9.3 9 15 9.9 8 26 17.2 7 31 20.5 6 13 8.6 5 18 11.9 4 16 10.6 3 12 7.9 2 3 2.0 1 1 0.7 0 2 1.3

Grouped Frequency Table:

You decide how many intervals to use, but make them equal intervals!

Frequency Graphs Histogram

Used for continuous data, so bars can touch

Bar graph used for categorical data – bars don’t touch.

Frequency Graphs Frequency polygon

Like a histogram, but use points instead of bars May indicate change over time better

Shapes of Frequency Distributions

Unimodal, bimodal, and rectangular

Shapes of Frequency Distributions

Symmetrical and skewed distributions Which direction is the tail pointing? Pos/Neg?

Shapes of Frequency Distributions Normal and kurtotic distributions

Indicates variability of the scores – clustered or spread out?

SPSS Example: Data Entry & Frequencies

• 1. Open SPSS, choose “Type in Data” when starting a new data file.– Notice the spreadsheet has 2 tabs at the bottom: “data

view” and “variable view”.– Data view = where you enter your data and use the menus

to analyze data– Variable view = where you provide SPSS info about your

variables

SPSS Example: Data Entry & Frequencies

2. Start by clicking the “variable view” tab and we’ll give names to our variables

Things to note: Variable names have a max of 8 characters; don’t

use spaces or hyphens (underscores are OK) “labels” column - give more descriptive labels to

variables “type” column – default is numeric, change to

‘string’ if you use those variables

SPSS Example: Data Entry & Frequencies

“values” column – for numeric variables, can provide names for each value

3. Once variables are named, etc., click tab to go back to ‘data view’ and enter data.

4. What to do w/Missing data?

SPSS Example: Data Entry & Frequencies

• Once data is entered, begin analyses by using menus at top of ‘data view’ window.

5. For frequency tables, (AnalyzeDescriptives Frequencies) then click on arrow to get variables you want into ‘variable’ list.

• When analysis is done, SPSS takes you to a new ‘output’ window. Use the window buttons at bottom to move back & forth between output and data.

• Note – in tables, difference between “Percent” and “Valid Percent” depends on missing data –

– Use “Valid Percentage” to report %s & ignore missing data– Use “Percentage” to include all data, even if missing