2. – An experimental research hypothesis is an
assertion that systematic variation of
(1) an independent variable produces lawful
changes in
(2) a dependent variable.
– A critical characteristic of a sound research is
that
(3) the extraneous variables are controlled (or
addressed in some manner).
3. • Independent Variables
– Stimulus Variables
• In research, the independent variable is a stimulus, where the word
"stimulus" broadly refers to any aspect of the environment (physical,
social, and so on) that excites the receptors.
• When we use the term "stimulus," though, we actually mean a
certain stimulus class.
– Organismic Variables
• The possible relationships between organismic variables and
behavior are studied using the method of systematic observation
(or quasi-experiments) rather than experimentation.
• An organismic variable is any relatively stable physical
characteristic of an organism such as gender, eye color, height,
weight, and body build, as well as such characteristics as
intelligence, educational level, neuroticism, and prejudice.
4. • Dependent Variables
– Response Measures
• Since in psychology we’re interested in some aspect of
human or animal behavior, and since the components of
behavior are responses, our dependent variables are typically
(but not always) response measures.
• "Response measures" is also an extremely broad class that
includes such diverse phenomena as
– number of drops of saliva a person secretes when tasting
cheesecakes,
– number of errors an employee makes on a task,
– time it takes a person to solve a problem, amplitude of
electromyograms (electrical signals given off by muscles when
they contract),
– number of words spoken in a given period of time,
– accuracy of throwing a baseball, and
– judgments of people about certain traits.
5. • Accuracy. One way to measure response accuracy would bewith a
metrical system, such as when we fire a rifle at a target.
• Latency. This is the time that it takes from the onset of a stimulus to
the start of a response, as in reaction-time studies.
• Duration (Speed). This is a measure of how long it takes to
complete a response, once it has started.
– To emphasize the distinction between latency and duration measures:
latency is the time between the onset of the stimulus and the onset of the
response, and speed or duration is the time between the onset and
termination of the response, important differences indeed.
• Frequency and Rate. Frequency is the number of times a response
occurs, as in how many responses an organism makes before
extinction of a behavior.
• Additional Response Measures. Other examples are level of ability
that a person can manifest (e.g., how many problems of increasing
difficulty one solves with an unlimited amount of time) or the intensity
of a response (e.g., the amplitude of the galvanic skin response in an
emotional situation).
6. • The first requirement for a dependent variable - it must
be valid.
– By validity we mean that the data reported are actual
measures of the dependent variable as it is operationally
defined; that is, the question of validity is whether the
operationally defined dependent variable truly measures that
which is specified in the consequent condition of the
hypothesis.
• Reliability of Dependent Variables
– The second requirement is that a dependent variable should be
reliable.
– One meaning of reliability is the degree to which participants
receive the same scores when repeated measurements of
them are taken.
– A one-way affair: If there are statistically reliable differences
among groups, the dependent variable is probably reliable; if
there are no significant differences, then no conclusion about
its reliability is possible (at least on this information only).
7. – If replications of the experiment yield consistent results
repeatedly, certainly the dependent variable is reliable.
– Fundamental definitions are general in two senses:
They are universally accepted, and they encompass a
variety of specific concepts.
» A fundamental definition of anxiety would encompass
several specific definitions, with each specific
definition weighted according to how much of the
fundamental definition it accounts for. For instance,
each definition of anxiety may be an indicator of a
generalized, fundamental concept:
fundamental concept of anxiety = f(anxiety1, anxiety2, ... , anxietyN)
8. • General Types of Empirical Relationships
– There are two principal classes of empirical laws involving
independent variables:
(1) stimulus-response relationships which result from the use of the
experimental method and
(2) organismic-response laws which are derived from the use of the
method of systematic observation (quasi-experimental & correlational
approaches).
– Stimulus-Response Laws
• This type of law states that a certain response class is a function of a
certain stimulus class and may be symbolized as R =f(S).
• To establish an S-R law, a given stimulus is systematically varied as
the independent variable to determine whether a given response (the
dependent variable) also changes in a lawful manner.
– Organismic-Behavioral Laws
• This type of relationship asserts that a response class is a function of a
class of organismic variables, which is symbolized R = f(O).
• Research seeking to establish this kind of law aims to determine
whether certain characteristics of an organism are associated with
certain types of responses.
9. • The Nature of Experimental Control
– An Example...
– A sophisticated, but still ancient, investigation did include a control
condition: "Athenaeus, in his Feasting Philosophers (Deiphosophistae, III,
84-85), describes how it was discovered that citron was an antidote for
poison. It seems that a magistrate in Egypt had sentenced a group of
convicted criminals to be executed by exposing them to poisonous snakes
in the theater. It was reported back to him that, though the sentence had
been duly carried out and all the criminals were bitten, none of them had
died. The magistrate at once commenced an inquiry. He learned that
when the criminals were being conducted into the theater, a market
woman out of pity had given them some citron to eat. The next day, on
the hypothesis that it was the citron that had saved them, the magistrate
had the group divided into pairs and ordered citron fed to one of a pair but
not to the other. When the two were exposed to the snakes a second
time, the one that had eaten the citron suffered no harm, the other died
instantly. The experiment was repeated many times and in this way (says
Anthenaeus) the efficacy Of Citron as an antidote for poison was firmly
established" (Jones, 1964, p. 419).
10. – Two Kinds of Control of the Independent Variable
• There are two ways in which an investigator may exercise control of the
independent variable:
(1) purposive variation (manipulation) of the variable, and
(2) selection of the desired values of the variable from a number of values
that already exist.
• When purposive manipulation is used, an experiment is being conducted,
but selection is used in the method of systematic observation.
– If you are interested in whether the intensity of office lighting affects the rate of
processing, you might vary intensity in two ways - high and low.
» Since the stimulus is a light, such values as 2 and 20 candlepower might be
chosen.
» You would, then, at random:
(1) assign the sample of participants to two groups, and
(2) randomly determine which group would receive the low-intensity
stimulus, which one the high.
– In this case you are purposely varying (manipulating & controlling) the
independent variable (this is an experiment).
» The decision as to what values of the independent variable to study and,
more important, which group receives which value is entirely up to you.
» Perhaps equally important, you also "create" the values of the independent
variable.
11. • To illustrate control of the independent variable by selection of
values as they already exist (the method of systematic
observation), consider the effect of intelligence on problem-
solving.
– Assume that the researcher is not interested in studying the
effects of minor differences of intelligence but wants to study
widely differing values of this variable, such as an average IQ of
135, a second of 100, and a third of 65.
– Up to this point the procedures for the two types of control of the
independent variables are the same; the investigator determines
what values of the variables are to be studied.
– However, in this case, the investigator must find certain groups
that have the desired values of intelligence.
» The IQs of the people tested determined who would be the
participants.
» The researcher has not, as in the experimental example,
determined which participants would receive which value of
the independent variable.
– In selection it is thus the other way around: the value of the
independent variable determines which participants will be used.
12. • Techniques of Extraneous Variable Control
– The following common techniques illustrate major
principles that can be applied to a wide variety of
specific control problems.
• Elimination. The most desirable way to control extraneous
variables is simply to eliminate them from the research
situation.
– For example, some laboratories are sound deadened and opaque
to eliminate extraneous noises and lights. Other extraneous
variables that one would have a hard time eliminating are gender,
age, and intelligence.
13. • Constancy of Conditions. Extraneous variables that cannot be
eliminated might be held constant throughout the experiment.
– The same value of such a variable is thus present for all
participants.
» Perhaps the time of day is an important variable in that
people perform better on the dependent variable in the
morning than in the afternoon.
– One of the standard applications of the technique of holding
conditions constant is to conduct experimental sessions in the
same room.
» Thus, whatever might be the influence of the particular
characteristics of the room (gaiety, odors, color of the walls
and furniture, location), it would be the same for all
participants.
» In like manner, to hold various organismic variables constant
(educational level, sex, age), we would select participants
with the characteristics that we want.
– The technique of constancy of conditions dictates that all
participants use the same carousel projector, PowerPoint
presentation, recording apparatus, or other equipment.
14. • Balancing. When it is not feasible to hold
conditions constant, the experimenter may balance
out the effect of extraneous variables.
– Balancing may be used in two situations:
(1) where one is unable to identify the extraneous
variables, and
(2) where they can be identified and one takes special
steps to control them.
15. • Counterbalancing. In some experiments each
participant serves under two or more different
experimental conditions; for example, to determine
whether a stop sign should be painted red or
yellow, we might measure reaction times to them.
– The general principle of counterbalancing is that:
(1) in repeated treatment experiments, each condition
(e.g., color of sign) must be presented to each participant
an equal number of times, and each condition must occur
an equal number of times at each practice session.
(2) Furthermore, each condition must precede and follow
all other conditions an equal number of times.
16.
17. – The Problem of Differential Transfer
» Differential transfer means that the transfer from
condition 1 (when it occurs first) to condition 2 is
different from the transfer from condition 2 (when it
occurs first) to condition 1.
» In general, differential transfer reduces the recorded
difference between two conditions, but it may also
exaggerate the difference.
18. • Randomization. Randomization is a procedure
that assures that each member of a population or
universe has an equal probability of being
selected.
– Randomization is used as a control technique because
the experimenter takes certain steps to equalize effects
of extraneous variables on the different groups.
– Randomization has two general applications:
(1) where it is known that certain extraneous variables
operate in the experimental situation, but it is not feasible
to apply one of the preceding techniques of control, and
(2) where we assume that some extraneous variables
will operate, but cannot specify them and therefore
cannot apply the other techniques.
