Psych-Research Methods-Unit 3: Principles Of The Scientific Method: Validity And Control: Chapter 6: Validity

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1.Define internal validity.

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internal validity: extent to which a study provides evidence of a cause-effect relationship between the independent and dependent variables

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2.What is meant by confounding?

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confounding: error that occurs when the effects of two variables in an experiment cannot be separated, resulting in a confused interpretation of the results

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3.Why is confounding particularly acute in research in whicha subject variable is used?

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The problem of confounding is particularly acute in research in which the experimenter cannot control the independent variable—when partici- pants are selected according to the presence or absence of a condition and not selected simply to have a condition assigned to them. Such variables are called subject variables.

A good example of a subject variable is gender. Participants cannot be assigned to one gender, but must be selected from preexisting groups. When gender is one of the independent variables of an experiment, as it often is, we have a quasi experiment (see Chapter 13) and a much greater probability of confounding.

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4.Define construct validity.

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construct validity: extent to which the results support the theory behind the research

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5.Briefly describe the several ways to determine if a testhas construct validity.

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Construct validity is similar to internal validity. In internal validity, you strive to rule out alternative variables as potential causes of the behavior of interest; in construct validity, you must rule out other possible theoretical explanations of the results. In either case, you may have to perform another study to rule out a threat to validity. For internal validity, you may find it possible to redesign the study to control for the source of confounding. In the case of construct validity, you must design a new study that will permit a choice between the two competing theoretical explanations of the results.

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6.Define external validity.

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external validity: how well the findings of an experiment generalize to other situations or populations

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7.Define statistical conclusion validity.

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statistical conclusion validity: extent to which data are shown to be the result of cause-effect rela- tionships rather than accident

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8.What are the major threats to internal validity.

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In essence, guarding against threats to internal validity consists of learning to avoid the confounding of potentially important variables with the independent variable or variables of interest.

temporal precedence is important in determin- ing whether one thing caused another. The cause must always come before the effect, but in some cases, it is unclear in ambiguous temporal precedence. This often happens in correlational studies (see Chapters 8 and 9), in which two things are clearly related, but which one caused the other is not obvious.

Whenever an experiment is conducted in such a way that different experimental conditions are presented to subjects at different times, it is possible for events outside the laboratory to influence the results, and this type of confound is called history.

maturation: a source of error in an experiment related to the amount of time between measurements. Subjects may change between conditions of an experiment because of natu- rally occurring processes. This is particularly a problem in studies that involve children. Maturation is a more critical problem in research involving children because they change more rapidly over time than do adults.

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9.What is the regression effect? When does it arise?

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The regression effect, one of the most insidious threats to validity, arises in many situations. The regression effect operates when there is less than a perfect correlation between two variables.

The regression effect may occur when two different variables are correlated, such as SAT score and college GPA.

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10.What is mortality? When is it a threat to internalvalidity?

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mortality: the dropping out of some subjects before an experiment is completed, causing a threat to validity.

Mortality is a threat to validity because the partici- pants who drop out of a study may be different from those who complete it. Biases can result if particular kinds of participants drop out.

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11.Briefly describe two threats to construct validity.

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Loose Connection Between Theory and Method. Much psychological research suffers from poor operational definition of theoretical concepts.

Ambiguous Effect of Independent Variables. An experimenter may carefully design an experiment in which all reasonable confounding variables seem to be well controlled, only to have the results compromised because the participants perceive the situation differently than the experimenter does.

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12.Briefly describe three threats to external validity.

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Even if an experiment has internal validity, statistical conclusion validity, and construct validity, it may not be generalized to other situations. There are as many threats to the external validity of research as there are dimensions along which one experiment can differ from another.

We must not assume that any animal can be substituted for any other in all situations.

Many historical trends render particular research findings invalid, whether they concern use of lan- guage, attitudes toward foreign countries, or perception of deviant groups.

A pervasive problem that can hinder external validityinvolves the question of how the phenomenon observed in one laboratory can berelated to a similar phenomenon observed in another laboratory or in the realworld.

Though laboratory research ensures a higher level ofcontrol, it is sometimes not easy to decide if a certain effect is simply alaboratory effect or whether it would survive transplantation to the worldoutside the laboratory.

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13.What are the two broad categories of bias resulting fromthe interaction between subject and experimenter?

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The participants’ knowledge that they are participating in an experiment constitutes a set of expectations about how they are to behave. These expectations are called role demands, or demand characteristics, of the experiment.

Experimenter Bias. A large number of studies indicate that the experimenter can unintentionally bias the results of an experiment

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14.What are role demands (or demand characteristics)? Howmight they be overcome?

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Perhaps the most prevalent type of role demand is the good-subject tendency. Participants act the way they think the experimenter wants them to act. They may deliberately feign a naive attitude about the expected results even though they can guess the true purpose of the experiment.

Another kind of participant expectancy is the concern that the experimental procedure in some way measures the participant’s competence. Some participants are convinced that the experiment is a carefully disguised measure of intelligence or emotional adjustment. This expectancy gives rise to evaluation apprehension, in which participants tailor their behavior to make themselves look as normal as possible.

The most obvious and seemingly simplest solution is to deceive the subject about the experiment’s purpose. A cover story is devised that provides a plausible rationale, and the true hypothesis is not revealed. This ploy often works but has several drawbacks, not the least of which involves ethics.

An additional method of counteracting bias is to use a measure that is unlikely to be influenced by participants’ guesses about the hypothesis. Some examples might be such nonverbal behavior as how close people sit to one another or whether they look a person in the eye.

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15.What is experimenter bias? How might such a bias beovercome?

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Experimenter Bias. A large number of studies indicate that the experimenter can unintentionally bias the results of an experiment

The effects of experimenter bias are so ubiquitous that a standard procedure in many disciplines is for the experimenter to be “blind” to the condition a subject experiences. This method of preventing experimenter bias is excellent and fool- proof, but it is not always possible in a psychological experiment.

Another basic strategy for reducing experimenter bias is to standardize or automate experiments as much as possible. In some experiments, testing parti- cipants in all conditions at the same time may be possible. The various conditions can be induced by written instructions given to each subject. If participants must be tested individually, instructions can be tape-recorded or presented via computer, so that each subject receives the same experience. Variations on these basic strategies can be constructed for use in particular situations.