2 Experimental methodsOne of the most widely used methods in the study of behaviour is the experimentThe goal of an experiment is establish a cause-and-effect relationship between two variables.Experiments are performed under highly controlled conditions, in order to help determine cause and effect.Experiments are examples of quantitative research, which generates numerical data.
3 Overview of experimental variables Independent variableThe variable that causes a change in the other variable is called the independent variable(IV). This is the variable that the researcher will deliberately manipulate, while trying to keep all other variables constant.Dependent variableThe variable that is measured after the manipulation of the independent variable is called the dependent variable(DV).
4 DV and IV continuedFor example, you would like to find out if noise affects one’s ability to recall information.The aim of the study is to see if one variable– noise—has an effect on another variable—recall of informationIndependent variable is manipulated: noise or no noiseDependent variable is measured: number of words recalledControl confounding variables
5 Variables continued Variables must be operationalized to be measured. This means that you must have an operational definition. It must be written in such a way that it is clear what is being measured.In our previous experiment, noise might be defined as high music played at 35 volume and results might be defined as number of words recalled from a list of 20
6 Experimental research To formalize the aim, the researcher formulates a hypothesis. The hypothesis is a prediction of how the independent variable affects the dependent variable.An experimental hypothesis predicts the relationship between the IV and the DV—that is what we expect will come out of the manipulation of the independent variable
7 Experimental method continued In our noise experiment, there are two conditions. One condition where the participants must recall a list of words with very loud music. The second condition where participants recall words with no music. This is called the control condition, because we compare the two conditions in order to see if there is a difference.
8 Experimental hypothesis Experimental predicts the relationship between the variables.Example: Noise will decrease the number of words that an individual is able to recall from a listIV is predicted to have an effect on DVNull hypothesisIt is conventional to create a null hypothesis also.The null hypothesis states that the IV will have no effect on the DV, or that any change in DV is due to chance.Example: Noise has no effect on an individual’s ability to recall a list of words; or, any change in the individual’s ability to recall a list of words is due to chance
9 Null hypothesis Why have a null hypothesis? The researcher wants to refute the null hypothesis to show that the predicted cause-and-effect relationship between IV and DV exists.Sometimes, the researcher must accept the null hypothesis. For example, if there was no apparent relationship between noise and recall. Nothing can be proven—only disproven. The goal is to either accept the null hypothesis, or refute the null hypothesis.
10 Different types of experiments Laboratory experiments: strict controls, easier to replicate, artificial and therefore participants may react differently than in real life. Ecological validity—the extent to which the results predict behavior outside the laboratory—is critical in laboratory experimentsField experiments: takes place in a natural environment, but researchers still manipulate the variables. It has ecological validity but researchers are unable to control all variables.
11 Different types of experiments A natural experiment is an experiment where the researchers have no control over the variables. The variables are naturally occurring.For example: stroke victims or children kept in isolation
12 Points to consider with experiments Confounding variables: undesirable variables that influence the relationship between the IV and the DV. Examples are:Demand characteristics: participants act differently because they know that they are in an experiment. Known as the Hawthorne effect. They may try to guess the aim of the study and attempt to alter the results to match the aim. A single blind study is one way to counteract the Hawthorne effect.
13 Points continuedResearcher bias: also called observer bias, occurs when the experimenter sees what he or she is looking for. The researcher’s expectations affect the findings of the study. A double blind control may help avert this. Neither the researcher nor the participant knows which group is the control group and which group is the treatment group.Participant variability: characteristics of the sample affect the dependent variable. This can be alleviated by using a random sample or by randomly allocating or assigning people to the treatment group or the control group.
14 Cross-cultural validity Ecological validityEcological validity means that the study represents what happens in the real world. If in a laboratory experiment, people do things that we know they would never do in real life, the study is said to lack ecological validity. Or if an experiment is so well controlled that all normal influences upon behaviour were eliminated, it is said to lack ecological validity.Cross-cultural validityCross-cultural validity means that the research is relevant to other cultures. If it is not , it is said to be ethnocentric—based on the values and beliefs of one culture.