1. Variable
It is a concept—a noun that stands for variation within a class of objects, such as chair, gender, eye color, achievement, motivation, running speed, even ‘spunk’, ‘style’ and ‘lust for life’ are variables.

2. Constant
If all members of a class are identical, we don’t have a variable. Such characteristics are called constants.
Since the individual members of the class are not allowed to vary, but rather are held constant.

3. Kinds of variables Independent and dependent variables
Quantitative variables
Categorical variables
Manipulated variables
Outcome variables
Extraneous variables

4. Independent & dependent variables
Independent variable is presumed to affect is called the dependent variable.
The nature of dependent variable “depends on” what the independent variable does to it, how it affects it.

5. Example
A researcher studying the relationship between childhood success in mathematics and adult career choice is likely to refer to the former as the independent variable and subsequent career choice as the dependent variable, even though success is not manipulated.

6. Example
“Will students who are taught by a team of three teachers learn more science than students taught by one individual teacher?”
Independent variable is the number of teachers.
Amount of science learning is dependent.

7. Quantitative variables
They exist in some degree along a continuum from “less” to “more”.
They can often be subdivided into smaller and smaller units. For example, “Length” can be measured in miles, yards, feet, inches, etc.

8. Categorical variables
They do not vary in degree, amount, or quantity but are qualitatively different.
For example, eye color, gender, religious preference, etc.

9. Find out quantitative and categorical variables.
Make of automobile
Learning ability
Ethnicity
Cohesiveness
Heartbeat rate
Gender

10. Manipulated and outcome variables
Whenever researchers set up an experiment along the lines of the examples in which there are two or more experimental conditions, they create a variable.
Such variables are called experimental, manipulated or treatment variables.

11. Outcome variable
An outcome is a result of some sort, an observed behavior, product, that has been stimulated in some way.
For example “Will students who are taught by a team of three teachers learn more science than students taught by one individual teacher?” What’s outcome variable in this question?(amount of science learning)

12. Extraneous Variables
In a research many possible independent variables having an effect on the dependent variables.
These are called extraneous variables.
Task is to control these extraneous variables somehow to eliminate or minimize their effect.
Extraneous are independent variables and need to be controlled smartly.