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scientific method A five-step process for empirical investigation of a hypothesis under conditions designed to control biases and subjective judgements empirical intestigation An approach to research that relies on sensory experience and observations as research data theory A testable explanation for a set of facts or observations. In science, a theory is not just speculation or a guess. Hypothesis A statement predicting the outcome of a scientific study; a statement describing the relationship among variables in a study operational definitions Specific descriptions of concepts involving the conditions of a scientific study. Operational definitions are stated in terms of how the concepts are to be measured or what operations are being employed to produce them. Independent variable A stimulus condition so named because the experimenter changes it independently of all the other carefully controlled experimental conditions Random presentation A process by which chance alone determines the order in which the stimulus is presented. Data Pieces of information, especially information gathered by a researcher to be used in testing a hypothesis. Dependent Variable The measured outcome of a study; the responses of the subjects in a study. Replicate In research, this refers to doing a study over to see whether the same results are obtained. As a control for bias, replication is often done by someone other than the researcher who performed the original study. Experiment A kind of research in which the researcher controls all the conditions and directly manipulates the conditions, including the independent variable. Confounding/Extraneous variables Variables that have an unwanted influence on the outcome of an experiment. Controls Constraints that the experimenter places on the experiment to ensure that each subject has the exact same conditions. Random assignment Each subject of the sample has an equal likelihood of being chosen for the experimental group of an experiment. Ex post facto Research in which we choose subjects based on a pre-existing condition. Correlational study A type of research that is mainly statistical in nature. Correlational studies determine the relationship (or correlation) between two variables. Survey A quasi-experimental method in which questions are askede to subjects. When designing a survey, the researcher has to be careful that the questions are not skewed or biased toward a particular answer. Naturalistic Observation A research method in which subjects are observed in their natural environment Longitudinal Study A type of study in which one group of subjects is followed and observed for an extended period of time. Cross-sectional Study A study in which a representative cross section of the population is tested or surveyed at one specific time. Cohort-sequential study A research method in which a cross section of the population is chosen and then each cohort is followed for a short period of time. Personal Bias The researcher allowing personal beliefs to affect the outcome of a study. Expectancy bias The researcher allowing his or her expectations to affect the outcome of a study. double-blind study An experimental procedure in which both researchers and participants are uninformed about the nature of the independent variable being administered. Institutional Review Board A committee at each institution where research is conducted to review every experiment for ethics and methodology. Institutional Animal care and Use Committee A committee at each institution where research is conducted to review every experiment involving animals for ethics and methodology. Frequency distribution A summary chart, showing how frequently each of the various scores in a set of data occurs. Histogram A bar graph depicting a frequency distribution. The height of the bars indicates the frequency of a group of scores Descriptive Statistics Statistical procedures used to describe characteristics and responses of groups of subjects. Mean The measure of central tendency most often used to desrcibe a set of data--Calculated by adding all the scores and dividing by the number of scores. Median The measure of central tendency for a distribution, represented by the score that separates the upper half of the scores in a distribution from the lower half. Mode A measure of central tendency for a distribution, represented by the score that occurs more often than any other. Range The simplest measure of variability, represented by the difference between the highest and lowest values in a frequency distribution. Standard Deviation A measure of variability that indicates the average difference between the scores and their mean. Normal Distribution A bell-shaped curve, describing the spread of characteristics throughout a population. Correlation A relationship between variables, in which changes in one variable are reflected in changes in the other variable--as in the correlation between a child's age and height. Correlation coefficient A number between -1 and 1 expressing the degree of relationship between two variables. Inferential statistics Statistical techniques used to assess whether the results of a study are reliable or whether they might be simply the result of chance. Used to determine whether two or more groups are essentially the same or different. Random sample A sample group of subjects selected by chance. Representative sample A sample obtained in such a way that it reflects the distribution of important variables in the larger population in whichc the researchers are interested. Significant difference Psychologists accept a difference between the groups as "real" or significant, when the probability it might be due to an atypical sample drawn by chance is less than 5 in 100. (p<.05)