Variables is a central idea in research, in simple, a variable is a concept that varies. A variable is something that can change, such as ‘gender’ and are typically the focus of a study. Variables are those simplified portions of the complex phenomena that a researcher intend to study. The word variable is derived from the root word “vary”, meaning, changing in amount, volume, number, form, nature or type. These variables should be measurable, i.e., they can be counted or subjected to a scale. In other words, a Variable is a measurable characteristic that varies. It may change from group to group, person to person, or even within one person over time. There are two main types of variables-independent and dependent.

Dependent Variable

A dependent variable shows the effect of manipulating or introducing the independent variables. For example, if the independent variable is the use or non-use of a new language teaching procedure, then the dependent variable might be students’ scores on a test of the content taught using that procedure. In other words, the variation in the dependent variable depends on the variation in the independent variable.

Independent Variable

Independent variables are variables which are manipulated or controlled or changed.  In the example “a study of the effect of teacher praise on the reading achievement  of  second-graders”,  the effect of praise, the researcher is trying to determine whether there is a cause-and-effect relationship, so the kind of praise is varied to see whether it produces different scores on the reading achievement test.

Examples of independent and dependent variables:

Example 1: 

A study of teacher-student classroom interaction at different levels of schooling.

Independent variable:  Level of schooling, four categories – primary, upper primary, secondary and junior college.

Dependent variable: Score on a classroom observation inventory, which measures teacher – student interaction 


These refer to abstract processes that are not directly observable but that link the independent and dependent variables. In language learning and teaching, they are usually inside the subjects’ heads, including various language learning processes which the researcher cannot observe. For example, if the use of a particular teaching technique is the independent variable and mastery of the objectives is the dependent variable, then the language learning processes used by the subjects are the intervening variables.


These affect the relationship between the independent and dependent variables by modifying the effect of the intervening variable(s). Unlike extraneous variables, moderator variables are measured and taken into consideration. Typical moderator variables in TESL and language acquisition research (when they are not the major focus of the study) include the sex, age, culture, or language proficiency of the subjects.


Language learning and teaching are very complex processes. It is not possible to consider every variable in a single study. Therefore, the variables that are not measured in a particular study must be held constant, neutralized/balanced, or eliminated, so they will not have a biasing effect on the other variables. Variables that have been controlled in this way are called control variables.


These are those factors in the research environment which may have an effect on the dependent variable(s) but which are not controlled. Extraneous variables are dangerous. They may damage a study’s validity, making it impossible to know whether the effects were caused by the independent and moderator variables or some extraneous factor. If they cannot be controlled, extraneous variables must at least be taken into consideration when interpreting results.

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