Glossary Items Starting with "M"
 magnitude
 A characteristic of the abstract number system in which the
numbers have an inherent order.
 main effects
 In a
factorial design, main effects refer to the
individual effects of the independent variables. In contrast,
interaction effects are the combined effects of two or more
independent variables on the dependent variable.
 mainstream psychology
 Contemporary psychology, which is largely an integration of
many of the earlier schools of psychology and their theoretical
models.
 manipulated factors
 Independent variables in a factorial design in which the
levels of the factors are determined by active manipulation by
the experimenter.
 manipulated
independent variable
 Type of independent variable found in an experimental
research study. When manipulated independent variables are used,
participants are randomly assigned to groups or conditions.
 manipulation
 The explicit control of the independent variable by the
researcher.
 manipulation check
 Procedure designed to verify that the independent variable
varied in the different groups or conditions. A manipulation
check is independent of any evaluation of the effect of the
independent variable on the dependent variable.

MannWhitney Utest
 A nonparametric inferential statistic used to test the
difference between two groups when the dependent measure
produces ordinal data.

matchedpairs ttest
 See
correlated ttest.
 matched random
assignment
 Experimental procedure used to insure that groups are
equivalent at the beginning of the study. In matched random
assignment, participants are matched in small groups (size is
determined by the number of conditions in the study) on relevant
variables, and each member of the matched group is randomly
assigned to one of the conditions of the study until all members
have been assigned to one condition. Matched random assignment
is an alternative to a withinsubjects design and should be used
whenever significant
sequence effects can be expected in a withinsubjects
design.
 matchedsubjects design
 Research design in which participants are matched on a
variable that is highly correlated with the dependent measure.
Once matched, each participant is randomly assigned to each of
the groups defined by the independent variable. The design helps
control for individual differences without introducing the
sequence effects inherent in a withinsubjects
design.
 materials subsection
 See
apparatus subsection.
 matrix of cells
 Structure of cells in a
factorial design.
 maturation
 Potential confounding factor involving changes in
participants on the dependent measure during the course of the
study that results from normal growth processes.
 mean
 Arithmetic average of scores. The mean is the most commonly
used measure of
central tendency but should be computed only for
score data.
 mean square
 In analysis of variance (ANOVA), the mean square is a
variance estimate. Several different mean squares are computed
in any ANOVA. It is the ratio of mean squares that is the
Fratio.
 measurement error
 Any inaccuracy found in the measurement of a variable.
Although it is impossible to determine the precise degree and
direction of measurement error for a given participant, it is
possible to specify the average error associated with a
particular measure.
 measurement reactivity
 Any effect on the participant's behavior that results from
the participant being aware that he or she is being observed.
Measurement reactivity can be reduce by using
unobtrusive measures.
 measures subsection
 See
apparatus subsection.
 measures of central
tendency
 Descriptive statistics that indicate the typical score.
 median
 Middle score in a distribution.
 mentalistic
 Based on the subject experience of a person rather than
objective behavior.
 metaanalysis
 A procedure that allows the statistical averaging of results
from independent studies of the same phenomena. Metaanalyses
essentially combine studies on the same topic into a single
large study, providing an index of how strongly the independent
variable affected the dependent variable in the set of studies.
 method section
 The section of the research report that details the nature
of the sample and the procedures used in the study.
 microcannulae
 Tiny tubes that can be surgically implanted in animals.
These tubes allow the animal to function normally, with no pain
or discomfort, while at the same time allowing researchers to
study brain functioning by delivering specific chemicals to
specific regions of the animals brain to see their impact on
functioning.
 microdialysis
 A procedure similar to microiontophoresis except that the
tiny tubes are actually one tube inside of another, with the
outer tube having a porous tip. This permits the researcher to
pump substances through the tube, allowing the natural chemicals
of the brain to be sampled through the porous end of the tube.
This process permits researchers to see what chemicals are
produced and active in specific brain regions while the animal
is performing specific tasks and, thus, helps researchers to
understand potential biological mechanisms behind specific
behavior.
 microiontophoresis
 A procedure involving the implantation of tiny tubes or
microcannula into specific regions of the brains of
animals. This process can be done without causing pain to the
organism. It allows the researcher to deliver specific chemical
substances to specific regions of the brain in order to see what
impact the chemicals have on the functioning of the animal.
 Minitab
 Computer package for statistical analysis of data.
 mixed designs (between and
withinsubjects variables)
 Factorial design in which at least one of the factors is a
betweensubjects factor and at least one of the factors is a
withinsubjects factor. The pattern of between and
withinsubjects factors affects the selection of the statistical
analysis.
 mixed designs (manipulated
and nonmanipulated variables)
 Factorial design in which at least one of the factors
represents a nonmanipulated independent variable and at least
one of the factors represents a manipulated independent
variable. The distinction between manipulated and nonmanipulated
variables does not affect the data analysis. However, the
interpretation of the results must take into account the fact
that at least some of the factors are nonmanipulated factors
and, therefore, represent differential research.
 mode
 Most frequent score in a distribution.
 models
 In science, models are representations of the complex
reality of the real world.
 moderator variable
 Any variable that has an effect on the observed relationship
between two or more other variables. When a moderator variable
is operating, it is best to measure the relationship between
variables separately in subgroups defined by the moderator
variable. For example, relationships between variables are often
evaluated separately in males and females (a commonly used
moderator variable).
 Monte Carlo study
 A procedure that evaluates the effectiveness of statistical
tests by simulating with a computer the repeated sampling of
participants from a population with known parameters. The
characteristics of the populations can be systematically varied
to see what effect these variations have on the accuracy of the
statistical decision. This process allows one to determine
empirically the probability of Type I and Type II errors to see
the strength of the impact of violations of the assumptions of
statistical procedures.
 mouse
 A device for moving the cursor on the screen of a personal
computer. Sliding the mouse on a table moves the cursor, and
clicking the buttons on the mouse performs various tasks.
 multidimensional scaling
 A group of statistical methods that are used to simplify
data by finding a small number of dimensions or factors that
collectively account for most of the variability in a group of
scores.

multilevel, completely randomized, betweensubjects design
 A research design, using more than two groups, in which
participants are randomly assigned to groups and each
participant appears in only one group.
 multiple baseline design
 Research design often used with single participants when one
wants to infer a causal relationship between the independent and
dependent variables. Baselines on several different behaviors
are taken, and treatment strategies are applied at different
points in time to each behavior being monitored.
 multiplechoice items
 In a questionnaire, each question or item is presented with
several answers from which the respondent chooses one.
 multiple correlation
 A correlation in which a criterion is correlated with a set
of variables. The correlation is computed by finding the linear
combination of the set that will provide the highest possible
correlation with the criterion.
 multiple observers
 Control used to evaluate the accuracy of observations made
by two or more independent observers.
 multivariable design
 See
factorial design.

Multivariate Analysis of Variance (MANOVA)
 Extension of analysis of variance in which two or more
dependent measures are simultaneously evaluated.
 multivariate
correlational designs
 Correlational designs that include more than two variables.
 multivariate techniques
 Advanced statistical procedures used to evaluate complex
relationships among several variables.