Psych Chapter 2

hindsight bias

the tendency to believe, after learning an outcome, that one would have foreseen it. (Also known as the I-knew-it-all-along phenomenon.)

hypothesis

a testable prediction, often implied by a theory.

operational definition

a carefully worded statement of the exact procedures (operations) used in a research study. For example, human intelligence may be operationally defined as what an intelligence test measures.

replication

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.

case study

a descriptive technique in which one individual or group is studied in depth in the hope of revealing universal principles.

naturalistic observation

observing and recording behavior in naturally occurring situations without trying to manipulate and control the situation.

survey

a technique for ascertaining the self-reported attitudes or behaviors of a particular group, usually by questioning a representative, random sample of the group.

sampling bias

a flawed sampling process that produces an unrepresentative sample.

population

all those in a group being studied, from which samples may be drawn.

random sample

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

correlation

a measure of the extent to which two variables change together, and thus of how well either variable predicts the other.

correlation coefficient

a statistical index of the strength of a relationship between two variables (from -1 to +1).

scatterplot

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).

illusory correlation

the perception of a relationship where none exists.

experiment

a research method in which an investigator manipulates one or more factors (independent variables) to observe the effect on some behavior or mental process (the dependent variable). By random assignment of participants, the experimenter aims to control other relevant variables.

experimental group

in an experiment, the group exposed to the treatment, that is, to one version of the independent variable.

control group

in an experiment, the group not exposed to the treatment; contrasts with the experimental group and serves as a comparison for evaluating the effect of the treatment.

random assignment

assigning participants to experimental and control groups by chance, thus minimizing preexisting differences between the different groups.

double-blind procedure

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.

independent variable

the experimental factor that is manipulated; the variable whose effect is being studied.

confounding variable

a factor other than the independent variable that might produce an effect in an experiment.

dependent variable

the outcome factor; the variable that may change in response to manipulations of the independent variable.

validity

the extent to which a test measures or predicts what it is supposed to.

descriptive statistics

numerical data used to measure and describe characteristics of groups. Includes measures of central tendency and measures of variation.

histogram

a bar graph depicting a frequency distribution.

mode

the most frequently occurring score(s) in a distribution.

mean

the arithmetic average of a distribution, obtained by adding the scores and then dividing by the number of scores. Most affected by outliers.

median

the middle score in a distribution; half the scores are above it and half are below it. Best measure when there are outliers.

skewed distribution

a representation of scores that lack symmetry around their average value - outliers.

range

the difference between the highest and lowest scores in a distribution.

standard deviation

a computed measure of how much scores vary around the mean score.

normal curve (normal distribution)

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

inferential statistics

numerical data that allow one to generalize—to infer from sample data the probability of something being true of a population.

statistical significance

a statistical statement of how likely it is that an obtained result occurred by chance.

informed consent

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

debriefing

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

placebo effect

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.

false consensus effect

the tendency to overestimate the extent to which others share our beliefs and behaviors

confirmation bias

a tendency to search for information that supports our preconceptions and to ignore or distort contradictory evidence

belief perseverance

clinging to one's initial conceptions after the basis on which they were formed has been discredited