Experimental Methods

Experimental method

• Involves the manipulation of an independent variable (IV) to measure the effect on the dependent variable (DV)

• Experiments may be laboratory, field, natural, or quasi

Aim

• A general statement of what the researcher intends to investigate; the purpose of the study.

• For example: "To investigate whether drinking energy drinks makes people more talkative"

Hypothesis

• A clear, precise, testable statement that states the relationship between the variables to be investigated. Stated at the start of any study

• For example: "Drinking energy drinks causes people to become more talkative"

Null hypothesis

A statement that predicts no difference or correlation in results.

Alternative hypothesis

A statement that predicts difference or correlation in results.

Directional hypothesis

• States the direction of the difference or relationship. Includes words like more or less, higher or lower, faster or slower, etc

• For example: "People who drink energy drinks become more talkative than people who don't" "People who drink water are less talkative than people who drink energy drinks"

Non-directional hypothesis

• Does not state the direction of the difference or relationship. The nature of the difference is not specified

• For example: "People who drink energy drinks differ in terms of talkativeness compared with people who don't drink energy drinks"

How would I chose my hypothesis for this study?

Researchers tend to use a directional hypothesis when a theory or the findings of previous research studies have suggested a particular outcome. However, when there is no previous research or findings then the research may decide to use a non-directional hypothesis.

Independent variable (IV)

• Some aspect of the experimental situation that is manipulated by the researcher - or changes naturally- so the effect on the other variable can be measured

Dependent variable (DV)

• The variable that is measured by the researcher. Any effect on this variable should be caused by the change in the other variable

Levels of the IV

In order to test the effect of the IV we need to use an experimental method. We need a comparison. 

• Experimental condition

• Control condition

Operationalisation of variables

• Clearly defining variables in terms of how they can be measured

• For example, a hypothesis that has gone through this would be: "After drinking 300ml of energy drinks, participants say more words in the next five minutes than participants who drink 300ml of water"

Co-variables

An IV and DV are only used in experiments as they are looking for cause and effect (a difference). 

When correlations (relationships) are investigated, we call the variables co-variables. 

One does not necessarily affect the other, they are just related in some way.