Item
Response Theory: Lab Session
Learning
to use Testgraf software
Set
up of raw data can follow one of two formats:
·
For
either format, enter data in another program, like SPSS, and save it as a .dat
file.
·
The
data must contain only variables to be analyzed in Testgraf98 and must omit
column headings.
1.
Traditional
set up in Testgraf
First
line:
number of items and number of characters of label (participant ID)
use 0 if there are no labels
Second
line
exam key with label characters, if any, coming first
Other
lines
responses of participants in the same pattern as the key
For
omitted responses, in the raw data file, you can leave the space blank or chose
a special character.
Example:
10
2
00
1273725343
01
2736275213
02
7376255463
03
26173 5342
*Note the blank space indicates an omitted response
04
7526256462
2.
Raw
data
·
Data
for subject 1 begins on the first row, followed by data for other subjects
·
There
are no labels indicating how the data is set up.
Basic
Commands in order of operation:
To
open Testgraf
Start - run - open -
type “c:\testgraf98.exe” - ENTER
You
will be given 6 options at the top of the window
Choose the New option as instructed below
To
open a new dataset
data must be in a .dat file entered in the proper form
NEW - type filename.dat - ENTER
You are given boxes to complete only if you have not
set up the data as indicated below
title: 2 lines are available
#items
length of character labels
#lines per subjects
item type (multiple choice or scale)
character representing omitted responses
Click on OK when you are completed.
Tesgraf saves the data in several files used below
To
edit the new dataset
EDIT - type filename.tgn - OPTIONS/ITEMS – QUIT
The file to open must have the tgn extension
*OPTIONS: to view or change weights given to
each option and
check frequencies
*ITEMS: to change item label, list the correct
option, or change item type
(multiple
choice or scale)
-QUIT at each prompt to exit the edit mode
To
analyze the data
ANALYZE - type filename.tgn
The default options are suggested so
click
OK to get pass the options
Testgraf will tell you when it finishes
You are now ready to create graphs
To
create graphs
DISPLAY - type filename.tga
A menu of options is displayed
One option is SELECT DISPLAY VARIABLE which
allows you to choose to display the graph for the
expected score or standard normal
The expected score is the default
We use the expected score only for displaying the
distribution of scores
- QUIT to exit
To
print
DISPLAY – OPTION – PRINT to print option
characteristic curve plot
DISPLAY – ITEM – PRINT to print item plot
DISPLAY – TOGGLE PRINT OF PLOTS –
click
all plots to print