I - J

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• Institutional Review Board (IRB)

  The group who looks at the ethical standards of all research that involves studying people.
  

• independent variables

  Something that causes change in something else (the “dependent variable”). The independent variable is the one changed by the researcher to see what will happen to the dependent variable(s).
  

• index

  A measure of something or how strong something is, how often it happens, or when it changes. For instance, how dark the circles under a person’s eyes are can be an index of how he or she is sleeping.
  

• inductive method

  A way of making general statements based on individual examples, rather than starting with the general statements and drawing examples from those.
  

• informed consent

  An agreement to take part in research which is based on a full explanation and understanding of why the research is being undertaken and any impact or effects it might have on participants. How you obtain informed consent is a major ethical consideration in research, especially with people who are mentally confused or who have a learning disability.
  

• inferential statistics

  A method that allows researchers to make judgments about a whole population by using examples from a smaller part (a sample) of that population.
  

• interaction effects

  Changes in a dependent variable that are caused by two or more independent variables that act together.
  

• internal consistency

  A measure of how well items of a scale or test are linked to each other, whether they belong together and are pulling in the same direction.
  

• internal validity

  A measure of how well a study accounts for and controls all the other differences (that are not related to the study question) among the people being studied. An internally valid study usually requires a “control group” and “random assignment.” In an experiment, this kind of validity means the degree to which changes that are seen in a dependent variable can be linked to changes in the independent variable.
  

• interval scale

  A scale with points that are equally distant from each other, but without an absolute zero point; for example, the Celsius temperature scale.
  

• intervention

  A planned change; for example, a new therapy or a new medication; or the act of making this change.