chapter 9 notes

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19 Dec 2010
Chapter 9: Conducting Experiments
Selecting research participants
-Samples may be drawn from the population using probability sampling or
nonprobability sampling techniques
-When it is important to accurately describe the population, you must use
probability sampling
-Much research, however, is more interested in testing hypotheses about
behaviour. Here, the focus of the study is the relationships between the variables
being studied and testing predictions derived from theories of behaviour. In such
cases, the participants may be found in the easiest way possible using
nonprobability haphazard or “convenience” sampling methods
-In general, increasing your sample size increases the likelihood that your results
will be statistically significant because larger samples provide more accurate
estimates of population values
Manipulating the independent variable
-To manipulate an independent variable, you have to construct an operational
definition of the variable. That is, you must turn a conceptual variable into a set of
operations – specific instructions, events, and stimuli to be presented to the
research participants
-In addition, the independent and dependent variables must be introduced within
the context of the total experimental setting. This has been calledsetting the
Setting the stage
-In setting the stage, you usually have to do two things: (1) provide the participants
with the informed consent information needed for your study and (2) explain to
participants why the experiment is being conducted.
-If participants know what you are studying, they may try to confirm the
hypothesis, or they may try to look good by behaving in the most socially
acceptable way
-If you find that deception is necessary, you have a special obligation to address
the deception when you debrief the participants at the conclusion of the
-How the variable is manipulated depends on the variable and the cost, practicality,
and ethics of the procedures being considered
Types of manipulations
(1) straightforward manipulations
-Straightforward manipulations manipulate variables with instructions and
stimulus presentations. Stimuli may be presented verbally, in written form, via
videotape, or with a computer
-Examples on pg 167-168
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-Most manipulations of independent variables in all areas of research are
(2) staged manipulations
-Sometimes, it is necessary to stage events that occur during the experiment in
order to manipulate the independent variable successfully. When this occurs, the
manipulation is called a staged or event manipulation
-Staged manipulations are most frequently used for two reasons
-(1) the researcher may be trying to create some psychological state in the
participants, such as frustration, anger, or a temporary lowering of self-esteem (2)
a staged manipulation may be necessary to stimulate some situation that occurs in
the real world
-Staged manipulations frequently employ a confederate (sometimes termed an
“accomplice”). Usually the confederate appears to be another participant in an
experiment but is actually part of the manipulation. A confederate may be useful
to create a particular social situation
-Asch was able to demonstrate how easy it is to produce conformity – participants
conformed to the unanimous majority on many of the trials even though the
correct answer was clear. Confederates may be used in field experiments as well
as laboratory research (Asch line test and conformity)
-Staged manipulations are used to involve the participants in an ongoing social
situation, which the individuals perceive not as an experiment but as a real
experience. Researchers assume that the result will be natural behaviour that truly
reflects the feelings and intentions of the participants
-Difficult for other researchers to replicate the experiment. Also, a complex
manipulation is difficult to interpret. If many things happened during the
experiment, what one thing was responsible for the results?
-Easier to interpret results when the manipulation is straightforward. However, the
nature of the variable you are studying sometimes demands complicated
Strength of the manipulation
-The simplest experimental design has two levels of the independent variable
-In planning the experiment, the researcher has to choose these levels. A general
principle to follow is to make the manipulation as strong as possible
-A strong manipulation maximizes the differences between the two groups and
increases the chances that the independent variable will have a statistically
significant effect on the dependent variable
-Example on page 171: amount of similarity = strength of manipulation of ind var
-A strong manipulation is particularly important in the early stages of research,
when the researcher is most interested in demonstrating that a relationship does,
in fat exist
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-If the early experiments reveal a relationship between the variables, subsequent
research can systematically manipulate the other levels of the independent
variable to provide a more detailed picture of the relationship
-The principle of using the strongest manipulation possible should be tempered by
at least two considerations. First, the strongest possible manipulation may involve
a situation that rarely, if ever, occurs in the real world
-A second consideration is ethics: a manipulation should be as strong as possible
within the bounds of ethics. A strong manipulation of fear or anxiety, for
example, might not be possible because of the potential physical and
psychological harm to participants
Cost of the manipulation
-Cost is another factor in the decision about how to manipulate the independent
-A manipulation that uses straightforward presentation of written or verbal
material is less costly than a complex, staged, experimental manipulation
-Some government and private agencies offer grants for research; because much
research is costly, continued public support of these agencies is very important
Measuring the dependent variable
Types of measures
-The dependent variable in most experiments is one of three general types: self-
report, behavioural, or physiological
(1) self-report measures
-Self-reports can be used to measure attitudes, liking for someone, judgements
about someone’s personality characteristics, intended behaviours, emotional
states, attributions about why someone performed well or poorly on a task,
confidence in one’s judgements, and many other aspects of human thought and
behaviour. Rating scales with descriptive anchors (end points) are most
commonly used.
oStrongly disagree _ _ _ _ _ _ _ Strongly agree
(2) Behavioural measures
-Behavioural measures are direct observations of behaviours
-As with self-reports, measurements of an almost endless number of behaviours
are possible. Sometimes, the researcher may record whether or not a given
behaviour occurs. Often, the researcher must decide whether to record the number
of times a behaviour occurs in a given time period – the rate of a behaviour; how
quickly a response occurs after a stimulus – a reaction time; or how long a
behaviour lasts – a measure of duration
-Sometimes, the nature of the variable being studied requires either a self-report or
a behavioural measure. For many variables, however, both self-reports and
behavioural measures could be appropriate. When both options are possible, a
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