SOCY 210 - Experiments

Experiment

A systematic attempt to test a causal hypothesis about the effect of one variable on another variable

Key Components of a Classical Experiment

IV and DV

Pre-testing and post-testing

Experimental and control groups

The experimenter’s control (ability to manipulate) of the IV

Pre-Test

Initial measurements of the dependent variable prior to introduction of the independent variable (experimental stimulus)

Post-Test

Follow-up measurements of the dependent variable after introduction of the independent variable

Experimental Group

Exposed to the treatment, policy or initiative being manipulated

Control Group

Group not exposed to the experimental manipulation

Artificial Experiment

Experiment conducted under highly controlled, artificial conditions (e.g., online, a psychology laboratory)

Field Experiment

An experiment conducted in real world conditions

True Experiment

Experiment in which the experimenter manipulates the IV and assigns cases to treatment or control conditions randomly

Quasi Experiment

Experiment in which the experimenter manipulates the IV but cases are not assigned to conditions randomly

Do not use random assignment of cases to attributes of the IV

Natural Experiment

Experimental approximation in which an event, policy, or circumstance created comparison conditions in which the experimenter does not manipulate the IV or randomly assign cases, but simply observes the resulting differences

Double-Blind Experiment

Experiment in which both subjects and experimenters do not know which subjects are in the experimental group or the control group, group assignment is tracked to compare group differences, but in a way that reduces the impact of researcher subjectivity

Experimenters can pre-judge results when they are anticipating a certain effect

Dichotomous Variable

A variable that has only two attributes; also called a binomial variable

Hawthorne Effect

Researchers discovered that their presence affected the behaviour of the individuals being studied, any impact of researcher on the subject of study

Random Assignment

The procedure of randomly assigning experimental subjects to experimental and control groups, such that each subject has an equal probability of being in either group

Ensures that the subjects exposed to the test are as comparable as possible to those exposed to the control factor

Matching

Procedure whereby pairs of subjects are matched on the basis of their similarities on one or more variables; then one member of the pair is assigned to the experimental group and the other to the control group

Is a way to achieve comparability between experimental and control groups

Internal Invalidity

Refers to the possibility that the conclusions drawn from experimental results may not accurately reflect what went on in the experiment itself

Threat is present whenever anything other than the experimental stimulus can affect the dependent variable

Sources of Internal Invalidity

History, Maturation, Testing, Instrumentation, Statistical Regression, Selection Biases, Experimental Mortality, Causal Time Order, Diffusion or Imitation of Treatments, Compensation, Compensatory Rivalry, Demoralization

Sources of Internal Invalidity - History

During the course of the experiment, historical events may occur that will confound the experimental results

Sources of Internal Invalidity - Maturation

In a long-term experiment, the fact that subjects grow older may have an effect

In a short-term experiment, they may grow tired, sleepy, bored or hungry, or change in other ways that may affect their behaviour in the experiment

Sources of Internal Invalidity - Testing

Process of testing + retesting will influence people’s behaviour, thereby confounding the experimental results

Sources of Internal Invalidity - Instrumentation

If experimenters are making the measurements, their standards or abilities may change over the course of the experiment

Sources of Internal Invalidity - Statistical Regression

Danger that changes occurring by virtue of subjects starting out in extreme positions will be attributed erroneously to the effects of the experimental stimulus

Sources of Internal Invalidity - Selection Biases

Comparisons don’t have any meaning unless the groups are comparable

Sources of Internal Invalidity - Experimental Mortality

Experimental subjects may drop out of the experiment before it’s completed, which can affect statistical comparisons and conclusions

Sources of Internal Invalidity - Causal Time Order

Ambiguity about the time order of the experimental stimulus and the dependent variable can arise

Whenever this occurs, the research conclusion that the stimulus causes the dependent variable can be challenged with the explanation that the “dependent” variable actually caused changes in the stimulus

Sources of Internal Invalidity - Diffusion or Imitation of Treatments

When experimental and control-group subjects can communicate with each other, experimental subjects could pass on some elements of the experimental stimulus to the control group

Sources of Internal Invalidity - Compensation

In experiments in real-life situations, subjects in the control group are often deprived of something considered to be of value - in such cases, there may be pressures to offer some form of compensation; in such a situation, control group is no longer a genuine control group

Sources of Internal Invalidity - Compensatory Rivalry

In real-life experiments, the subjects deprived of the experimental stimulus may try to compensate for the missing stimulus by working harder

Sources of Internal Invalidity - Demoralization

Feelings of deprivation within the control group may result in their giving up

In educational experiments, demoralized control-group subjects may stop studying, act up, or get angry

External Invalidity

Refers to the possibility that conclusions drawn from experimental results may not be generalizable to the “real” world

Solomon Four-Group Design

Design that addresses the problem of testing interaction with the stimulus, involves four groups of subjects assigned randomly from a pool

Labelling Theory

Addresses the phenomenon of people acting in accord with the ways they are perceived and labelled by others

Pygmalion Effect

Differences in study outcomes attributable to the researcher’s expectations of participants

When researchers believe in an individual's potential, that individual often works harder and achieves more to meet those positive expectations