- random number generator
- A computer function that generates an endless sequence of
random numbers.

- random order of presentation
- This is a way of controlling for
*carry-over effects*in within-subjects designs. Each participant is tested under all conditions, but the order of the conditions is randomly determined for each participant.

- random samples
- Samples that are drawn using random sampling techniques.

- random sampling
- Procedure for the selection of participants in which each
participant has an equal chance of being selected and the
selection of any one participant will not affect the probability
of selecting any other participant. In most research, random
sampling from the population is not feasible. Instead,
researchers rely on sampling from an
*accessible population*.

- randomization
- Any procedure that assigns a value or order in an
unpredictable or random way, such as by use of tables of random
numbers. Randomization procedures may be used for selecting
participants, assigning participants to groups or conditions, or
assigning the order in which a participant will experience a
number of successive conditions.

- randomize within blocks
- A control procedure to reduce
sequence effects, which involves using a block of one trial
from each condition and randomizing participant assignment to
these conditions before going on to the next block.

- randomized, posttest-only, control-group design
- Experimental design in which participants are randomly
assigned to two groups, and each group is tested on the
dependent variable after the independent variable manipulation.

- randomized, pretest-posttest, control-group design
- Experimental design in which participants are randomly
assigned to two groups, and each participant is tested on the
dependent variable both before and after the manipulation of the
independent variable.

- range
- Distance between the lowest score and the highest score.

- ratio scale
- Scale of measurement in which the intervals between scores
are equal and the zero point on the scale represents none of the
quality being measured (a true zero). Examples of ratio scales
are height, weight, and frequency of an event.

- rationalism
- A way of knowing about the universe that relies on
systematic logic and a set of premises from which logical
inferences are made.

- reactive measure
- Any measurement procedure that produces different scores
depending on whether participants are aware they are being
measured.

- records (in computer files)
- Each record typically represents all of the data for a
single participant or for a group of matched participants.

- reference
- The listing of a source of information (e.g., research
article, book, chapter, etc.) that contributed to a research
paper. The
*APA Publication Manual*lists specifications for how to list a reference so that others can quickly find it.

- reference list
- The listing of a source of information (e.g., research
article, book, chapter, etc.) that contributed to a research
paper. The
*Publication Manual of the American Psychological Association*lists specifications for how to list a reference so that others can quickly retrieve it for review.

- reference section
- The section of a research report that follows the
substantive sections of the report and lists each of the papers
and articles that contributed to the ideas and procedures of the
study described in the report.

- regression
- A mathematical procedure that produces an equation for
predicting a variable (the
*criterion measure*) from one or more other variables (the*predictor measures*). The procedures for determining the regression equation are designed to maximize the accuracy of the prediction. Linear regression equations are usually used, although it is possible to develop non-linear regression equations.

- regression equation
- The mathematical equation that predicts the value of one
variable from one or more other variables.

- regression to the mean
- Potential confounding variable that occurs whenever
participants are selected because of extreme scores (either very
high or very low). When retested on the same or similar
variable, the original extreme sample tends to be less extreme
on average.

- reification of a construct
- Incorrectly accepting a construct as a fact.

- relationship
- Any connection between two or more variables. In research,
there are many types of relationships, from contingencies to
causal relationships.

- relative score
- See
*standard score*.

- reliability
- Index of the consistency of a measuring instrument in
repeatedly providing the same score for a given participant.
There are many different types of reliability, each referring to
a different aspect of consistency. Types of reliability include
*interrater reliability*,*test-retest reliability*, and*internal consistency reliability*.

- repeated-measures ANOVA
- Statistical procedure to evaluate the mean differences
between two or more conditions in which participants are tested
under each condition. The repeated-measures ANOVA takes into
account the fact that the same participants appear in all
conditions.

- repeated-measures design
- Any research design in which participants are tested more
than once. Examples of such designs are
*pretest-posttest designs*,*within-subjects designs*, and time-series designs.

- repeated-measures factorial
- Factorial design in which all factors are within-subjects
factors. Each participant is tested under every possible
combination of conditions in the design.

- repeated-measures factorial ANOVA
- The statistical procedure for analyzing the results of a
factorial study in which all factors are within-subjects
factors.

- replicate
- See
*replication*.

- replication
- To repeat a study with no changes in the procedure (
*exact replication*), small theory driven changes (*systematic replication*), or changes in the operational definitions of variables (*conceptual replication*).

- representative sample
- Sample of participants that adequately reflects the
characteristics of the population from which the sample was
drawn.

- representativeness
- Degree to which a sample is representative of the population
from which the sample was drawn.

- research data
- See
*data*.

**research design checklist**- An assessment of a research design procedures prior to data
collection.

- research ethics
- Set of guidelines designed to protect human and nonhuman
participants from the risks of participating in research.

- research hypothesis
- Precise and formal statement of a research question. The
research hypothesis is constructed by adding
*operational definitions*for each of the variables to the*statement of the problem*.

- research setting
- Any characteristics of the situation and/or surroundings in
which a research project is carried out. Settings may vary from
natural, real-world settings to highly constrained and carefully
controlled laboratory settings.

- response-inferred organismic variable
- A hypothesized internal attribute of an organism that cannot
be directly observed but, instead, is inferred on the basis of
some observed behavior. Examples are intelligence, anxiety,
anger, and love.

- response-set bias
- Any tendency for participants to distort their responses to
a dependent measure. Response-set biases create
*measurement errors*.

- results section
- The section of a research report that describes the findings
and reports on the statistical analyses of the data.

- reversal design (ABA)
- Research design often used with single participants, in
which the effects of an independent variable on a dependent
variable are inferred from observations made first without the
independent variable present, then with the independent variable
present, and again without the independent variable present. If
an effect is noticed both when the independent variable is added
and when it is later removed, it is likely that the independent
variable is causally related to the dependent measure.

- rival hypothesis
- Any feasible alternative hypothesis to the
*causal hypothesis*.

- robust
- A statistical test is said to be robust to violations of the
assumptions on which the test is based if the test consistently
leads to accurate conclusions despite the assumption violations.

- row means
- In factorial designs, one factor is usually illustrated as
separate rows of data in which each row represents a different
level of the factor. A second factor is illustrated as columns
of data in which the different columns represent various levels
of the second factor. Row means are computed by taking the mean
of all participants who appear in a given row regardless of
their level on the second factor.