| variable | Anything that can change.
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| theory | A broad idea or set of closely related ideas that attempts to explain observations and to make predictions about future observations.
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| hypothesis | An educated guess that derives logically from a theory; a prediction that can be tested.
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| operational definition | A definition that provides an objective description of how a variable is going to be measured and observed in a particular study.
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| meta-analysis | A method that allows researchers to combine the results of several different studies on a similar topic in order to establish the strength of an effect.
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| descriptive research | Research that determines the basic dimensions of a phenomenon, defining what it is, how often it occurs, and so on.
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| case study or case history | An in-depth look at a single individual.
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| correlational research | Research that examines the relationships between variables, whose purpose is to examine whether and how two variables change together.
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| third variable problem | The circumstance where a variable that has not been measured accounts for the relationship between two other variables. Third variables are also known as confounds.
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| longitudinal design | A special kind of systematic observation, used by correlational researchers, that involves obtaining measures of the variables of interest in multiple waves over time.
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| experiment | A carefully regulated procedure in which the researcher manipulates one or more variables that are believed to influence some other variable.
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| random assignment | Researchers' assignment of participants to groups by chance, to reduce the likelihood that an experiment's results will be due to preexisting differences between groups.
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| independent variable | A manipulated experimental factor; the variable that the experimenter changes to see what its effects are.
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| confederate | A person who is given a role to play in a study so that the social context can be manipulated.
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| dependent variable | The outcome; the factor that can change in an experiment in response to changes in the independent variable.
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| experimental group | The participants in an experiment who receive the drug or other treatment under study—that is, those who are exposed to the change that the independent variable represents.
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| control group | The participants in an experiment who are as much like the experimental group as possible and who are treated in every way like the experimental group except for a manipulated factor, the independent variable.
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| external validity | The degree to which an experimental design actually reflects the real-world issues it is supposed to address.
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| internal validity | The degree to which changes in the dependent variable are due to the manipulation of the independent variable.
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| experimenter bias | Occurs when the experimenter's expectations influence the outcome of the research.
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| demand characteristics | Any aspects of a study that communicate to the participants how the experimenter wants them to behave.
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| research participant bias | Occurs when the behavior of research participants during the experiment is influenced by how they think they are supposed to behave or their expectations about what is happening to them.
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| placebo effect | Occurs when participants' expectations, rather than the experimental treatment, produce an outcome.
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| placebo | In a drug study, a harmless substance that has no physiological effect, given to participants in a control group so that they are treated identically to the experimental group except for the active agent.
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| double-blind experiment | An experimental design in which neither the experimenter nor the participants are aware of which participants are in the experimental group and which are in the control group until the results are calculated.
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| population | The entire group about which the investigator wants to draw conclusions.
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| sample | The subset of the population chosen by the investigator for study.
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| random sample | A sample that gives every member of the population an equal chance of being selected.
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| naturalistic observation | The observation of behavior in a real-world setting.
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| descriptive statistics | Mathematical procedures that are used to describe and summarize sets of data in a meaningful way.
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| mean | A measure of central tendency that is the average for a sample.
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| median | A measure of central tendency that is the middle score in a sample.
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| mode | A measure of central tendency that is the most common score in a sample.
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| range | A measure of dispersion that is the difference between the highest and lowest scores.
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| standard deviation | A measure of dispersion that tells us how much scores in a sample differ from the mean of the sample.
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| inferential statistics | Mathematical methods that are used to indicate whether results for a sample are likely to generalize to a population.
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