1.3 The Controlled Experiment in Detail

The variable that the researcher manipulates e.g. meditation or no meditation

The outcome variable that the researcher measures to determine whether manipulating the independent variable had an effect e.g. people’s scores on a mental wellbeing scale

A group of participants in a research study who are exposed to a particular manipulation of the independent variable

A group of participants in a research study who aren't exposed to the independent variable or a standard or placebo variation

Any variable other than the IV that may affect the DV

When an EV has systematically affected the DV because its influence is not evenly distributed across the levels of the IV

Variables that a researcher holds constant in an investigation

When scores are compared between different participants. One group is exposed to the experimental condition and the other group is exposed to the control condition.

There are no order effects

It assumes the groups are relatively similar on the range of extraneous variables that may affect the DV

Scores are compared within the same participants from different times. Each participant is exposed to both the experimental and control conditions.



Individual differences between people do not influence the results because each participant is compared to themselves



It is susceptible to the order effect. As each participant has to participate in both conditions, they engage in the testing procedure twice. The order effect can sometimes be overcome by counterbalancing.

A mix of both types of design is used, with both between subjects and within-subjects comparisons. In it's most simple form, a mixed design has two IVs, and each IV has two levels. One of the IVs is a between subjects variable, and the other IV is a within subjects variable.

It uses chance to determine how participants are assigned to groups e.g. using a random number generator to place participants into groups

When a researcher matches groups based on variables such as age or gender to control the effect of this variable

When random allocation to groups is not possible because the experimenter is interested in the effect of a characteristic that defines different groups of people e.g. if the researcher is studying the effect of meditation for people who experience anxiety compared to non-anxious people, then group allocation is defined by a person’s level of anxiety and cannot be random

When a participant's responses in various conditions are affected by the order of conditions to which they were exposed

When the order of conditions is split so not everybody completes the same conditions in the same order