by By Saul McLeod published 2012
An experiment is an investigation in which a hypothesis is scientifically tested. In an experiment, an independent variable (the cause) is manipulated and the dependent variable (the effect) is measured; any extraneous variables are controlled.
An advantage is that experiments should be objective. The views and opinions of the researcher should not affect the results of a study. This is good as it makes the data more valid, and less bias.
There are three types of experiments you need to know:
This type of experiment is conducted in a well-controlled environment – not necessarily a laboratory – and therefore accurate measurements are possible.
The researcher decides where the experiment will take place, at what time, with which participants, in what circumstances and using a standardized procedure. Participants are randomly allocated to each independent variable group.
Field experiments are done in the everyday (i.e. real life) environment of the participants. The experimenter still manipulates the independent variable, but in a real-life setting (so cannot really control extraneous variables).
An example is Holfing’s hospital study on obedience.
Natural experiments are conducted in the everyday (i.e. real life) environment of the participants, but here the experimenter has no control over the IV as it occurs naturally in real life.
For example, Hodges and Tizard's attachment research (1989) compared the long term development of children who have been adopted, fostered or returned to their mothers with a control group of children who had spent all their lives in their biological families.
The degree to which an investigation represents real-life experiences.
These are the ways that the experimenter can accidentally influence the participant through their appearance or behavior.
The clues in an experiment that lead the participants to think they know what the researcher is looking for (e.g. experimenter’s body language).
Variable the experimenter manipulates (i.e. changes) – assumed to have a direct effect on the dependent variable.
Variable the experimenter measures. This is the outcome (i.e. result) of a study.
All variables, which are not the independent variable, but could affect the results (DV) of the experiment. EVs should be controlled where possible.
Variable(s) that have affected the results (DV), apart from the IV. A confounding variable could be an extraneous variable that has not been controlled.
Randomly allocating participants to independent variable conditions means that all participants should have an equal chance of taking part in each condition.
The principle of random allocation is to avoid bias in the way the experiment is carried out and to limit the effects of participant variables.
Changes in participants’ performance due to their repeating the same of similar test more than once. Examples of order effects include:
(i) practice effect: an improvement in performance on a task due to repetition, for example because of familiarity of the task;
(ii) fatigue effect: a decrease in performance of a task due to repetition, for example because of boredom or tiredness.
McLeod, S. A. (2012). Experimental Method. Retrieved from www.simplypsychology.org/experimental-method.html