The experimental method

Uses random allocation of participants and the manipulation of variables to determine cause and effect.

A variable: any object, characteristic or event that varies in some way.

All procedures in an experiment should be standardised - kept the same for all participants.

In an experiment, a researcher manipulates an independent variable (IV) to see its effect on a dependent variable (DV).

Operationalisation: variables must be operationalised - this means clearly defining them so they can be manipulated and measured. You put a value on them, eg a number. Without accurate operationalisation, results would be unreliable and could not be replicated to check their reliability. 

These are variables other than the IV that might affect the DV.

Confounding variables: uncontrolled extraneous variables that negatively affect results.

3 main types of extraneous variable:

• Participant variables - eg pp's age and intelligence.
• Situational variables - the experimental setting and surrounding environment. eg temperature or sound.
• Experimenter variables - changes in personality, conduct and appearance in the researcher,       eg female researchers may gain different results to a male one.

Demand characteristics: Participants may change their behaviour if they know the true aim of the research. This can involve:

• guessing the purpose and trying the please the researcher
• guessing the purpose of the research and trying to annoy the researcher
• acting unnaturally out of nervousness/fear of evaluation
• acting unnaturally due to the social desirability bias

Investigator effects: the ways in which researchers consciously influence the results of research.

This can occur in several ways:

• physical characteristics of investigators may influence results, eg age or ethnicity
• less obvious personal characteristics, eg accent or tone of voice - pps may respond differently to someone with a stern voice
• investigators may be unconsciously biased in their interpretation of data and find what they expect to find

The double-blind procedure: a technique that reduces demand characteristics and investigator effects as it involves neither the pps or researchers knowing which condition of a study they are in. They are 'blind' to this knowledge.