Creating a Scale
Often times, to ensure validity and reliability, we don’t just ask one question for a particular concept like depression. Instead we ask quite a few questions that try to capture different facets of the concept of depression.
For example:
I feel sad …..
1. Never 2. Some days 3. Most days 4. Every day
I feel lonely ….
1. Never 2. Some days 3. Most days 4. Every day
I feel life is meaningless ….
1. Never 2. Some days 3. Most days 4. Every day
For each student, we can then take their average response across all 3 items above to get a better measure of their depression.
The three items above then make up what is known as a scale, i.e. a scale for depression.
You will also note that by taking the average across three items, our measure of depression is no longer discrete numbers of 1, 2, 3, and 4. But it now includes the range between 1 to 2, 2 to 3, 3 to 4 (e.g. 1.2, 2.6, 3.5, etc).
The Table on your right shows a scale for intrinsic motivation:
For example:
I feel sad …..
1. Never 2. Some days 3. Most days 4. Every day
I feel lonely ….
1. Never 2. Some days 3. Most days 4. Every day
I feel life is meaningless ….
1. Never 2. Some days 3. Most days 4. Every day
For each student, we can then take their average response across all 3 items above to get a better measure of their depression.
The three items above then make up what is known as a scale, i.e. a scale for depression.
You will also note that by taking the average across three items, our measure of depression is no longer discrete numbers of 1, 2, 3, and 4. But it now includes the range between 1 to 2, 2 to 3, 3 to 4 (e.g. 1.2, 2.6, 3.5, etc).
The Table on your right shows a scale for intrinsic motivation:
The video below illustrates how to use SPSS to test and determine if the scale you created has good reliability. We use "reliability" here slightly differently from what we talked about earlier. Here, we want to see if the items with our scale "hang-together" well. That is, how well do they measure an aspect of the same construct they are supposed to measure.
A higher alpha value would mean we have higher reliability that the items in our scale are measuring the same construct.
A higher alpha value would mean we have higher reliability that the items in our scale are measuring the same construct.
Likert scale
We need to distinguish "scale" (as described above) and "likert scale".
If you hear the term "Likert scale", this is usually referring to the answer options for a particular item. It's not referring to how the items come together to form a scale.
The format of a typical five-level Likert item, for example, could be:
1. Strongly disagree
2. Disagree
3. Neither agree nor disagree
4. Agree
5. Strongly agree
(see example from wikipedia on right)
Nonetheless, you may decide to create a 4-point Likert scale, or a 7-point scale, or a 10-point scale.
Dr B personally prefers a 4-point Likert scale (where possible).
If you hear the term "Likert scale", this is usually referring to the answer options for a particular item. It's not referring to how the items come together to form a scale.
The format of a typical five-level Likert item, for example, could be:
1. Strongly disagree
2. Disagree
3. Neither agree nor disagree
4. Agree
5. Strongly agree
(see example from wikipedia on right)
Nonetheless, you may decide to create a 4-point Likert scale, or a 7-point scale, or a 10-point scale.
Dr B personally prefers a 4-point Likert scale (where possible).
Testing Understanding
For students who have accessed to an online library, feel free to click on the link below. (Click on the study topic in blue).
The role of friends in early adolescents' academic self-competence and intrinsic value for math and English
(or copy the link below and paste in your browser:
http://link.springer.com/article/10.1007%2Fs10964-007-9266-3)
See if you can determine:
1. How many items made up the scale for "Intrinsic value for English"
2. How many points was the Likert scale for each item?
Answers: 4, 7
The role of friends in early adolescents' academic self-competence and intrinsic value for math and English
(or copy the link below and paste in your browser:
http://link.springer.com/article/10.1007%2Fs10964-007-9266-3)
See if you can determine:
1. How many items made up the scale for "Intrinsic value for English"
2. How many points was the Likert scale for each item?
Answers: 4, 7