Variables variable
Independent variable (IV): Variable the experimental manipulates - assumed to have a direct effect on the dependent variable.
Dependent variable (DV):Variable the experimental measures, after making changes to the IV which are assumed to affect the DV.
Extraneous variables (Ex Vs): Other variables, apart from the IV, that might affect the DV. They might be important enough to provide alternative explanations for the effects, for example, confounding variables.
Independent variables (IV): variables manipulated by the experimenter-assumed to have direct effects on the dependent variable.
Passive Variable (DV): A variable measured by the experimenter, which is assumed to affect the DV after changing the IV.
External Variables (Ex Vs): Other variables that may affect DV in addition to IV. They may be important enough to provide additional explanations for the effects, for example, confounding variables.
Types of experiments Types of experiments
Laboratory experiment: Artificial environment with tight controls over variables.
Field experiment: Natural environment with Independent variable manipulated by researchers.
Natural experiment: Natural changes in independent variable are used - it is not manipulated.
Laboratory experiment: artificial environment, strict control of variables.
Field experiment: natural environment, independent variables are manipulated by researchers.
Natural Experiment: Natural Changes of using independent variable - it is not manipulated.
Note: In a true experiment participants are randomly allocated to groups.
Note: In the real experiment, participants were randomly assigned to each group.
Strengths and weaknesses of experimental methods Advantages and weaknesses of experimental methods
Laboratory experiments Laboratory experiments
Strengths Advantages: | Weaknesses Weaknesses: |
Tighter control of variables. Easier to comment on cause and effect. has more strict control over variables. It is easier to comment on causality. | demand characteristics - participants aware of experiment, may change behavior. Requirement characteristics-Participants realize that experiments may change behavior. |
Relatively easy to replicate. is relatively easy to copy. | Artificial environment - low reality. Artificial environment-low reality. |
Enable use of complex equipment. can use complex devices. | May have low ecological validity - difficult to generalise to other situations. may have low ecological validity--hard to generalise to other situations. may have low ecological validity--hard to generalize to other situations. |
Often cheaper and less time-consuming than other methods. is usually cheaper and more time-saving than other methods. . | Experimenter effect - bias when experimenter's expectations affect behavior. Experimenter effect--When experimenter's expectations affect behavior, bias will occur. |
Field experiments
A field experiment takes place anywhere in a natural setting; it could take place in a school, hospital, the street or an office.
Note Note:
A field experiment is an experiment; the independent variable is manipulated. Not all field studies are experiments.
Field experiment is an experiment; independent variables are manipulated. Not all field studies are experiments.
Strengths Advantages: | Weaknesses Weaknesses: |
People may behave More naturally than in laboratories - higher reality. People's behavior may be more natural-realistic than in the laboratory. | Often only weak control of extraneous variables - difficult to replicate. usually only weak control of irrelevant variables - difficult to copy. |
Easier to generalise from results. is easier to summarize from the results. | Can be time-consuming and costly. can be time-consuming and costly. |
Natural experiments Natural experiments
Strengths Advantages: | Weaknesses Weaknesses: |
Situations in which it would be ethically unacceptable to manipulate the independent variable. manipulating independent variables is ethically unacceptable. | The independent variable is not controlled by the experimenter. independent variable is not controlled by the experimenter. |
Less chance of demand characteristics or experimenter bias interfering. Demand characteristics or experimentalist bias interference less chances. | No control over the allocation of participants to groups (random in a 'true experiment'). has no control over the grouping of participants (random in "real experiment"). |
Experimental design Experimental design
Three experimental designs are commonly used Three experimental designs are commonly used:
Independent groups: Testing separate groups of people, each group is tested in a different condition.
Repeated measures: Testing the same group of people in Different conditions, the same people are used repeatedly.
Matched pairs: Testing separate groups of people - each member of one group is same age, sex, or social background as a member of the other group.
In each case, there are one or more experimental groups, where the independent variable has changed and a control group where the independent variable has not changed.
Independent group: test different populations, each group is tested under different conditions.
repeated measurements: test the same group of people under different conditions and reuse the same people.
matched pair: Test different populations--each member of one group has the same age, gender, or social background as members of another group.
In each case, there are one or more experimental groups, where independent variables have changed, and a control group, where independent variables have not changed.
Advantages and disadvantages for each experimental design
Independent groups:
Avoids order effects.If a person is involved in several tests they man became bored, tired and fed up by the time they come to the second test, or becoming wise to the requirements of the experiment!
More people are needed than with the repeated measures design.
Differences between participants in the groups may affect results, for example; variations in age, sex or social background. These differences are known as participant variables.
avoids the order effect. If a person has participated in several tests, then when they reach the second test, they will feel bored, exhausted and bored, or the requirements for the experiment become wise! This is the benefit of independent groups.
requires more people than repeat measurement design.
The differences between participants in each group may affect the results, for example, changes in age, gender, or social background. These differences are referred to as participant variables.
Repeated measures Repeated measurements:
Avoids the problem of participant variables.
Fewer people are needed.
Order effects are more likely to occur.
avoids the problem of participant variables.
requires less people.
sequential effect is more likely to occur.
Matched pairs:
Reduces participant variables.
Avoids order effects.
Very time-consuming trying to find closely matched pairs.
Impossible to match people exactly, unless identical twins!
reduces the variables for participants.
avoids the order effect.
is time consuming to try to find a close match.
Unless it is identical twins , it is impossible to match exactly!
Note Note:
Counterbalancing: Alternating the order in which participants perform in different conditions of an experiment. For example, group 1 does 'A' then 'B', group 2 does 'B' then 'A' this is to eliminate order effects.
Randomisation: Material for each condition in an experiment is presented in a random order, this is also to prevent order effects.
equilibrium method: the order of participants is executed alternately under different conditions of the experiment. For example, the first group does "A" first and then "B", and the second group does "B" first and then "A", which is to eliminate the order effect.
Randomization: The materials for each condition in the experiment are presented in a random order, which is also to prevent the order effect.
