Chapter 2

standard deviation

The most widely used measure of variation of data; an index of the amount of variability in a set of data; a computed measure of how much scores vary around the mean score

critical thinking

Thinking that does not blindly accept arguments and conclusions. Rather, it examines assumptions, discerns hidden values, evaluates evidence, and assesses conclusions.

normal distribution

a bell-shaped curve, describing the spread of a characteristic throughout a population. In a normal distribution, half the scores fall at or above the mean and half the scores fall at or below the mean.

random sample

a sample that fairly represents a population because each member has an equal chance of inclusion

positively skewed distribution

contains a preponderance of scores on the low end of the scale. The mean will be higher than the median in a positively skewed distribution. The median is thus a better representation of central tendency than the mean in a positively skewed distribution.

sampling bias

exists when a sample is not representative of the population from which it was drawn

statistical significance

exists when the probability that the observed findings are due to chance is very low [less than the .05 level of significance, or less than 5 chances in 100]; a statistical statement of how likely it is than an obtained result occurred by chance.

correlation

exists when two variables are related to each other; a measure of the extent to which two factors vary together, and thus of how well either factor predicts the other

variability

how much the scores in a data set vary from each other and from the mean.

68-95-99.7 rule of normal distribution

in all score-based normal curves, 50% of the scores fall at or above the mean and 50% at or below the mean. Approximately 68% of all scores fall within one standard deviation of the mean, 95% within two standard deviations, and 99.7% within three standard deviations

experimental group

in an experiment, the group that is exposed to the treatment (to one version of the IV)

reliability

in testing, this refers to consistency or repeatability; subjects should answer questions the same way on two different occasions. A subject should also get the same score on a test on two different occasions.

validity

in testing, this refers to the extent to which the testing instrument measures or predicts what it is supposed to. (e.g., algebra questions would not be a valid measure of what was learned in history)

descriptive research

includes methods that enable researchers to observe and describe behaviors and mental processes without manipulating variables

zero correlation

indicates that there is no relationship between two variables

positive correlation

indicates that two variables more or vary in the same direction (e.g., smoking and lung cancer)

negative correlation

indicates that two variables move or vary in opposite directions (e.g., education level and expression of anger)

longitudinal method

measures a single individual or group of individuals over an extended period of time.

independent variable

a condition or event that an experimenter varies in order to see its impact on another variable; the experimental factor that is manipulated; the variable whose effect is being studied

scatter plot

a graphed cluster of dots, each of which represents the values of two variables. The slope of the points suggests the direction of the relationship between the two variables. The amount of scatter suggests the strength of the correlation (little scatter indicates high correlation)

correlation coefficient

a numerical index of the degree of relationship (strength and direction) between two variables; a statistical index of the relationship between 2 things (from -1 to +1)

journal

a periodical that publishes technical and scholarly material, usually in a narrowly defined area of inquiry

operational definition

a precise description of how the variable in a study will be manipulated and measured; describes the actions or operations that will be used to measure or control a variable

single-blind study

a procedure in which the subjects do not know whether they are in the experiment or control group

experiment

a research method in which the investigator manipulates a variable under carefully controlled conditions and observes whether any changes occur in a second variable as a result; a research method in which an investigator manipulates one or more factors (IVs) to observe the effect on some behavior or mental process (the DV). By random assignment of participants, the experimenter aims to control other relevant factors.

double-blind procedure

a research strategy in which neither participants nor experimenters know which subjects are in the experimental or control groups; an experimental procedure in which both the research participants and the research staff are ignorant (blind) about whether the research participants have received the treatment or a placebo. Commonly used in drug-evaluation studies.

naturalistic observation

a researcher engages in careful observation of behavior without intervening directly with the subjects; observing and recording behavior in naturally occurring situations without trying to manipulate and control the situation

measure of variation

a single score that presents information about the spread of scores in a distribution

survey

a study in which researchers use questionnaires or interviews to gather information about specific aspects of participants' background, attitudes, beliefs, or behavior; a technique for ascertaining the self-reported attitudes or behaviors of a particular group, usually by questioning a representative, random sampling of the group

normal curve (normal distribution)

a symmetrical, bell-shaped curve that describes the distribution of many types of data; most scores fall near the mean (68% fall within one standard deviation of it) and fewer near the extremes

theory

a system of interrelated ideas used to explain a set of observations; an explanation using an integrated set of principles that organizes observations and predicts behaviors or events.

social desirability bias

a tendency to give socially approved answers to questions about oneself

hypothesis

a tentative statement about the relationship between two or more variables; a testable prediction, often implied by a theory

informed consent

an ethical principle that research participants be told enough to enable them to choose whether they wish to participate

case study

an in-depth investigation of an individual subject; an observation technique in which one person is studied in depth with the hope of revealing universal principles.

variables

any measurable conditions, events, characteristics, or behaviors that are controlled or observed in a study

extraneous variables

any variables other than the independent variable that seem likely to influence the dependent variable in a specific study

cross-sectional method

compares individuals of various ages at one point in time.

negatively skewed distribution

contains a preponderance of scores on the high end of the scale. The mean will be lower than the median in a negatively skewed distribution. The median is thus a better representative of central tendency than the mean in a negatively skewed distribution.

experimenter bias

occurs when a researcher's expectations or preferences about the outcome of a study influence the results obtained (also called the experimenter expectancy effect)

reactivity

occurs when a subject's behavior is altered by the presence of an observer

random assignment of subjects

occurs when all subjects have an equal chance of being assigned to any group or condition in the study; assigning participants to experimental and control groups by chance, thus minimizing preexisting differences between those assigned to the different groups.

placebo effect

occurs when participants' expectations lead them to experience some change even though they receive empty, fake, or ineffectual treatment; experimental results caused by expectations alone; any effect on behavior caused by the administration of an inert substance or condition, which the recipient assumes is an active agent

confounding of variables

occurs when two variables are linked together in a way that makes it difficult to sort out their specific effects; the confounding (extraneous) variable is a factor other than the IV that might produce an unwanted effect on the outcome of an experiment.

anecdotal evidence

personal stories about specific incidents or experiences

participants

persons or animals whose behavior is systematically observed in a study; also known as subjects

data collection techniques

procedures for making empirical observations and measurements

internet-mediated research

studies in which data collection occurs over the web

mean

the arithmetic average of the scores in a distribution, obtained by adding the scores and then dividing by the number of scores

sample

the collection of subjects selected for observation in an empirical study

range

the difference between the highest and lowest scores in a distribution

population

the larger collection of animals or people from which the sample is drawn and which researchers want to generalize about; all the cases in a group being studied, from which the samples may be drawn. Does not refer to a country's whole population.

mode

the most frequently occurring scores in a distribution

debriefing

the post-experimental explanation of a study, including its purpose and any deceptions, to its participants

p-value

the probability of concluding that a difference exists when in fact the difference does not exist. The smaller the p-value, the more significant [not likely due to chance] are the results.

replication

the repetition of a study to see whether the earlier results are duplicated; repeating the essence of a research study, usually with different participants in different situations, to see whether the basic finding extends to other participants and circumstances

median

the score that falls exactly in the center of a distribution of scores; half the scores are above the median and half are below it

control group

the subjects who do not receive the special treatment given to the experimental group; in an experiment, the group that is not exposed to the treatment; contrasts with the experimental group and serves as a comparison for evaluating the effect of the treatment

statistics

the use of mathematics to organize, summarize, and interpret numerical data. Descriptive statistics are used to organize and summarize data. Inferential statistics are used to interpret data and draw conclusions.

dependent variable

the variable that is thought to be affected by manipulation of the independent variable; the outcome factor; the variable that may change in response to manipulations of the independent variable

inferential statistics

used to interpret data and draw conclusions

research methods

various approaches to the observation, measurement, manipulation, and control of variables in empirical studies