**Chapter II: Research Methods**

Scientific method is an empirical process in which a hypothesis is rigorously tested by careful experiment and observation.

Empirical investigation is a method of establishing new knowledge by making observations and drawing logical conclusions from obtained data.

Theory is a testable explanation for a set of facts.

Hypothesis, literally *little theory*, is a prediction of the result of a study which relates the variables can be falsified.

Operational definition is a part of an experiment or a study that specifies concepts and how they are to be quantified.

Independent variable is a part of an experiment that can be modified to produce results.

Dependent variable is the measured result of an experiment or a study that is produced by changing the independent variable.

Random presentation is a tool of a research psychologist in which he/she produces stimuli to the subject by chance alone.

Data is raw information collected from a study that will be analyzed later.

Replicate is to repeat the original experiment/study to ascertain whether its results are consistent and credible.

Experiment is a method of research in which the scientists directly control the conditions and modify the independent variable in order to produce an outcome.

Confounding/extraneous variables are things that influence the results of an experiment and are not accounted for in the procedure.

Controls are identical conditions a researcher imposes on his/her subjects during an experiment.

Random assignment is an experimental tool in which all possible subjects have equal probability of being put into a particular group.

Ex post facto is a quasi-experimental method in which subjects studied already have desired conditions.

Correlational study is a quasi-experimental method that uses statistics to determine the relationship between two variables. Note that correlation does not necessarily mean causation.

Survey is a quasi-experimental method that asks subjects specific questions.

Naturalistic observation is a quasi-experimental method in which subjects are observed in non-laboratory, i.e. natural, conditions.

Longitudinal study is a quasi-experimental method in which a chosen group of subjects is studied over an extended period of time.

Cross-sectional study is a quasi-experimental method in which a representative sample of a population is studied at one specific interval of time.

Cohort-sequential study is a quasi-experimental method in which a representative sample of a population is studied over a relatively short period of time.

Personal bias originates from the researcher’s beliefs and opinions and can affect his/her study’s results.

Expectancy bias originates from the researcher’s expectations and can affect his/her study’s results.

Double blind study is an experimental tool that prevents both the researchers and the subjects from knowing exactly what independent variable is being tested.

Frequency distribution is a measure of variability that shows how often each value in a set of data occurs.

Histogram is a bar graph that represents frequency distribution.

Descriptive statistics is a mathematical tool that characterizes the results of a study.

Inferential statistics is a mathematical tool that indicates the credibility of results from a study.

Mean is a measure of central tendency that is calculated by dividing the sum of all values within a set of data by the number of numbers.

Median is a measure of central tendency that is the number in the middle when all values within a data set are arranged in order of magnitude.

Mode is a measure of central tendency that is the number that occurs most often within a data set.

Range is a measure of variability that is the difference between the largest and smallest values of a data set.

Standard deviation is a measure of variability that is the average difference between the values of a data set and their (arithmetic) mean.

Normal distribution is a bell curve that represents the variability of values that occur in a data set.

Correlation is the relationship between two variables; when one changes, so does the other. Note that correlation does not necessarily mean causation.

Correlation coefficient is a number between -1 and +1 that describes the how strong the relationship between two variables are.

Random sample is a section of a population selected purely on the basis of chance.

Representative sample is a section of a population that accurately reflects that population.

Significant difference is a numerical value that indicates the probability that a result is due to chance.

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