Research In Psychology

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attrition

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a threat to the internal validity of a study; occurs when participants fail to complete a study, usually but not necessarily in longitudinal studies; those finishing the study may not be equivalent to those who stated it

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confound

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any extraneous variable that covaries with the independent variable and could provide an alternative explanation of the results

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construct validity

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in research, refers to whether the operational definitions used for independent and dependent variables are valid

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control group

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a group not given a treatment that is being evaluated in a study; provides a means of comparison

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dependent variable

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behavior measured as the outcome of an experiment

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ecological validity

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said to exist when research studies psychological phenomena in everyday situations (e.g., memory for where we put our keys.)

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experiment

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a research procedure in which some factor is varied, all else is held constant, and some result is measured

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experimental group

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in a study with an identified control group, the experimental group is given the treatment being tested

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external validity

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the extent to which the findings of a study generalize to other populations, other settings, and other times

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extraneous variable

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any uncontrolled factor that is not of interest to the researcher but could affect the results

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field experiment

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an experiment that is conducted outside of the laboratory; a narrower term than field research

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field research

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research that occurs in any location other than a scientific laboratory

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history

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a threat to the internal validity of a study; occurs when some historical event that could affect participants occurs between the beginning of a study and its end

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independent variable

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the factor of interest to the researcher; it can be directly manipulated by the experimenter (e.g., creating different levels of anxiety in subject) or participants can be selected by virtue of their possessing certain attributes (e.g., selecting two groups who differ in the normal levels of anxiousness)

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instructional variable

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type of independent variable in which participants are given different sets of instructions about how to perform (e.g., given stimuli, various groups might be told to process them in different ways).

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instrumentation

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a threat to the internal validity of a study; occurs when the measuring instrument changes from pretest to posttest (e.g., because of their experience with the instrument, experimenters might use it differently from pretest to posttest).

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internal validity

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the extent to which a study is free from methodological flaws, especially confounding factors

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maturation

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a threat to the internal validity of a study; occurs when participants change from the beginning to the end of the study simply as a result of maturational changes within them and not as a result of some independent variable

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posttest

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a measurement given to participants at the conclusion of a study after they have experienced a treatment or been in a control group; comparisons are made with pretest scores to determine if change occurred

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pretest

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a measurement given to participants at the outset of a study, prior to their being given a treatment (or not treated when subjects are in a control group).

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regression to the mean

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if a score on a test is extremely high or low, a second score taken will be closer to the mean score; can be a threat to the internal validity of a study if a pretest score is extreme and the posttest score changes in the direction of the mean

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situational variable

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type of independent variable in which subject encounter different environmental circumstances (e.g., large vs. small rooms in a crowding study).

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statistical conclusion validity

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said to exist when the researcher uses statistical analysis properly and draws the appropriate conclusions from the analysis

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subject selection

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a threat to the internal validity of a study; occurs when those participating in a study cannot be assigned randomly to groups; hence the groups are nonequivalent

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subject variable

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a type of independent variable that is selected rather than manipulated by the experimenter; refers to an already existing attribute of the individuals chosen for the study (e.g. gender)

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task variable

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type of independent variable in which participants are given different types of tasks to perform (e.g., mazes that differ in level of difficulty).

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testing

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a threat to the internal validity of a study; occurs when the fact of taking a pretest influences posttest scores, perhaps by sensitizing participants to the purpose of a study

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asymmetric transfer

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occurs when one sequence produces a transfer effect that is different from that produced by another counterbalancing sequence

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between-subjects design

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any experimental design in which different groups of particpants serve in the different conditions of the study

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block randomization

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a procedure used to accomplish random assignment and ensure an equal number of subjects in each condition; ensures that each condition of the study has a subject randomly assigned to it again; also used in within-subjects design as a counterbalancing procedure to ensure that when subjects are tested in each condition more than once, they experience each condition once before experiencing it again

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carryover effect

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form of sequence effect in which systematic changes in performance occur as a result of completing a sequence of conditions rather than a different sequence

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cohort effect

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a cohort is a group of people born at the same time; cohort effects can reduce the internal validity of cross-sectional studies because differences between groups could result from the effects of growing up in different historical eras

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complete counterbalancing

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occurs when all possible orders of conditions are used in a within-subjects design

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counterbalancing

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for a within-subjects variable, any procedute designed to control for sequence effects

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cross-sectional study

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in development psychology, a design in which age is the independent variable and different groups of people are tested; each group is of a different age

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demand characteristics

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any feature of the experimental design or procedure that increases the chances that participants will detect the true purpose of the study

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double-blind

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a control procedure designed to reduce bias; neither the participant nor the person conducting the experimental session knows which condition of the study is being tested; often used in studies evaluating drug effects

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equivalent groups

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groups of participants in a between-subjects design that are essentialy equal to each other in all ways except for the different levels of the independent variable

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evaluation apprehension

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a form of anxiety experienced by participants that leads them to behave so as to be evaluated positively by the experimenter

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experimenter bias

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occurs when an experimenter's expectations about a study affect its outcome

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good subject effect

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a form of participant bias in which participants try to guess the experimenter's hypothesis and then behave in such a way as to confirm it

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Hawthorne effect

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name often given to a form of participant bias in which behavior is influenced by the mere knowledge that the participant is in an experiment and is therefore of some importance to the experimenter

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latin square

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form of partial counterbalancing in which each condition of the study occurs equally often in each sequential position and each condition precedes and follows each other condition exactly one time

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longitudinal study

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in developmental psychology, a design in which age is the independent variable and the same group of people are tested repeatedly at different ages

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manipulation check

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in debriefing, a procedure to determine if subjects wre aware of a deception experiment's true purpose; also refers to any procedure that determines if systematic manipulations have the intended effect on participants

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matching

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a procedure for creating equivalent groups in which participants are measured on some factor (a "matching variable") expected to correlate with the dependent variable; groups are then formed by taking participants who score at the same level on the matching variable and randomly assigning them to groups

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matching variable

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any variavle selected for matching participants in a matched groups study

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partial counterbalancing

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occurs when a sub-set of all possible orders of conditions is used in a within-subjects design (e.g., a random sample of the population of all possible orders could be selected).

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participant bias

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can occur when the behavior of participants is influenced by their beliefs about how they are supposed to behave in study

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progressive effect

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in a within-subjects design, any sequence effect in which the accumulated effects are assumed to be the same from trial to trial (e.g., fatigue)

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random assignment

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the most common procedure for creating equivalent groups in a between-subjects design; each individual volunteering for the study has an equal probability of being asigned to any one of the groups in the study

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reverse counterbalancing

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occurs in a within-subjects design when participants are tested more than once per condition; subjects experience one sequence, then a second with the order reversed from the first (e.g., A-B-C-C-B-A)

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sequence (order) effect

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can occur in a within-subjects design when the experience of participating in one of the conditions of the study influences performance in subsequent conditions (see Progressive effect and Carryover effect)

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within-subjects design

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any experimental design in which the same participants serve in each of the different conditions of the study; also called a "repeated-measures" design

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ANOVA

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Short for ANalysis Of VAriance, the most common inferential statistical tool for analyzing the results of experiments when dependent variables are measured in interval or ratio scales

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continuous variable

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variable for which an infinite number of values potentially exists (e.g., a drug's dosage level)

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discrete variable

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variable in which each level represents a distinct category that is qualitatively different from another category (e.g., males and females)

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independent groups design

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a between-subjects design that uses a manipulated independent variable and has at least two groups of participants; subjects are randomly assigned to the groups

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matched groups design

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a between-subjects design that uses a manipulated independent variable and has at least two groups of participants; subjects are matched on some variable assumed to affect the outcome before being randomly assigned to the groups

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nonequivalent groups design

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a between-subjects design with at least two groups of participants that uses a subject variable or that creates groups that are nonequivalent

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nonlinear effects

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any outcome that does not form a straight line when graphed; can occur only when the independent variable has more than two levels

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placebo control group

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control group in which some participants believe they are receiving the experimental treatment, but they are not.

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repeated-measures design

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another name for a within-subjects design; participants are tested in each of the experiment's conditions

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single-factor multilevel design

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any design with a single independent variable and more than two levels of the independent variable

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t test for dependent groups

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an inferential statistical analysis used when comparing two groups in either a matched groups design or a repeated-measures design

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t test for independent groups

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an inferential statistical analysis used when comparing two groups in either an independent groups design or a non-equivalent groups design

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waiting list control group

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control group in which participants aren't yet receiving treatment but will eventually; used to ensure that those in the experimental and control groups are similar (e.g., all seeking treatment for the same problem)

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yoked control group

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control group in which the treatment given a a member of the control group is matched exactly with the treatment given a member of the experimental group