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unobtrusive (nonreactive) measures
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Measures of behavior that eliminate the problem of reactivity because observations are made in such a way that the presence of the observer is not detected by those being observed.
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physical traces
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Source of evidence that is based on the remnants, fragments, and products of past behavior; used as an alternative to or in conjunction with other research methods.
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Archival data
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Source of evidence based on records or documents relating the activities of individuals, institutions, governments, and other groups; used as an alternative to or in conjunction with other research methods.
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content analysis
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Any of a variety of techniques for making inferences by objectively identifying specific characteristics of messages, usually written communications but may be any form of message; used extensively in the analysis of archival data.
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selective deposit
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Bias that results from the way physical traces are laid down and the way archival sources are produced, edited, or altered, as they are established; when present, the bias severely limits generality of research findings.
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Internal validity
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Degree to which differences in performance can be attributed unambiguously to an effect of an independent variable, as opposed to an effect of some other (uncontrolled) variable; an internally valid study is free of confounds.
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selective survival
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Bias that results from the way physical traces and archives survive over time; when present, the bias severely limits the external validity of research findings.
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Independent groups design
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Each separate group of subjects in the experiment represents a different condition as defined by the level of the independent variable.
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random assignment
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Most common technique for forming groups as part of an independent groups design; the goal is to establish equivalent groups by balancing individual differences.
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random groups design
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Most common type of independent groups design in which subjects are randomly assigned to each group such that groups are considered comparable at the start of the experiment.
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Block randomization
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The most common technique for carrying out random assignment in the random groups design; each block includes a random order of the conditions and there are as many blocks as there are subjects in each condition of the experiment.
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threats to internal validity
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Possible causes of a phenomenon that must be controlled so a clear cause-effect inference can be made.
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Mechanical subject loss
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Occurs when a subject fails to complete the experiment because of equipment failure or because of experimenter error.
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selective subject loss
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Occurs when subjects are lost differentially across the conditions of the experiment as the result of some characteristic of each subject that is related to the outcome of the study.
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experimenter effects
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Experimenters’ expectations that may lead them to treat subjects differently in different groups or to record data in a biased manner.
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