Research Methods
Terminology
applied research—studies conducted to solve practical problems
basic research—studies of interest to psychology but not applicable to solving immediate, real-world
issues
replication—sufficient detail in the procedure section to duplicate the experiment with the same
materials and instructions
Variables
independent variable—what the experiment manipulates; commonly the experimental and control
groups
dependent variable—what is being measured; should be measurable with numbers
confounding variables—variables that are unintended and throw off the experimental results
counterbalancing—an attempt to spread out any ill effects of confounding variables
operational definition of variables—when an independent variable is defined according to the events
used to produce it (e.g. what constitutes “low anxiety” or “high anxiety”); a measured operational
definition applies to dependent variables that are defined in operational terms
research (or experimental) hypothesis—a detailed explanation of a predicted relationship between
certain conditions or variables; this hypothesis is not subject to change
null hypothesis—a detailed statement indicating there is no relationship between certain conditions or
variables
Validity and Reliability
reliability—the ability to produce consistent and stable scores or results
validity—the ability of a measuring instrument or experiment to measure what is intended
internal validity—controls prior influence, maturation processes and the order effect, but not the
subjects’ history with the task
external validity—controls the subjects’ history with the task but not the other aspects
Quantitative Research Methods
these methods are used by psychologists to test hypotheses under rigorous, controlled conditions
experiments take place in the laboratory or in the field
the aim is to establish a cause-and-effect relationship through descriptive and inferential statistics
statistics allow the researcher to determine the level of significance (at least at the .05 level)
Samples
population—the total number of people or things from which to draw a sample
sample—a small group of people or things selected to represent the target population
random sampling—selecting a sample from the population purely at random
representative sampling—occurs when the population is divided into subpopulations and then a
random sample is taken from each subpopulation
stratified sampling—a sample that matches the overall characteristics of the population from which it
is drawn
systematic sampling—a sample that is pulled from the population using a system or some criteria, such
as every 10th person
convenience sampling—participants are chosen based on availability (existing classes, individuals
walking into a store, participants at a self-help group)
independent subjects (between-subjects) design—a design in which groups of subjects experience
different experimental conditions; comparing a control group versus an experimental group is a
common independent samples design; measures two distinct groups
matched pairs design—a design where subjects are matched on one variable, and then one subject is
given one condition of the independent variable and the other subject is given the other condition
(usually experimental and control conditions)
repeated measures design (within-subjects design)—a design in which one group is measured before
and then after administration of a variable; typically this involves a pretest and a posttest
single participant/subject design—a design in which one subject’s performance over time or across
experimental conditions is tracked and recorded; this is not the same as a case study
Participant Controls
history—subjects have existing experience or skill involving the issue tested (e.g. a student has
attended study skills classes to help with memorization and the issue being examined involves
memorizing a list of terms)
selection bias—there is a systematic error in your sample (e.g. there is a disproportionate amount of
males versus females in your sample)
mortality—refers to subjects dropping out of the experiment part way through
maturation—refers to a change in the subject after the study begins (this is more likely if the
experiment is run over several days)
diffusion of treatment error—this occurs when subjects share information with one another outside
the study (e.g. students completing a math activity share their answer with subjects not yet being
tested)
order effects—an error in the order of experimental tasks (counterbalancing fixes this)
constancy of condition—a change in the room or conditions in the experiment (it’s always best to run
the study in the same location at the same time)
Ethical Considerations
there are five basic ethical considerations you need to address in any sort of research study:
 informed consent--subjects should be told briefly what will be involved in the psychological
experiment.
 justification for any discomfort or deception--you need to justify why you would cause a
subject any physical or mental discomfort, or deceive them in some way
 right of withdrawal--at all times, subjects have a right to withdraw from the experiment
 findings are confidential--while you can ask demographic information such as age, grade
level, sex, or GPA, you cannot record their names in connection with their results
 participants are debriefed--all subjects should be debriefed at the conclusion of your
experiment
Experimental Method
experimental group—a group that receives the experimental condition; the group that is affected by the
independent variable
control group—a group that does not receive the experimental condition; the group is not affected by
the independent variable
placebo group—a group that is a control group but receives a placebo to minimize subject bias (a
single blind experiment)
single-blind techniques—an experimental design in which subjects do not know which group they are
in, typically an experimental or control group; this reduces subject bias
double-blind techniques—an experimental design in which both the subjects and the experimenter do
not know which group is which; this reduces both subject and experimenter bias
research bias and expectancy (researcher and participant effects)—bias that occurs
demand characteristics—a cuing in process which insidiously instructs subjects in an experiment
about what is expected (e.g. compassionate behavior, aggressive behavior, etc); if deception is used as
to the purpose of the experiment, such subject bias arising out of demand should not occur
participant and researcher expectancies—based on the idea that what the researcher expects will alter
the subject’s performance; this is known as the Pygmalion effect; this was shown by Rosenthal’s study
that experimenter expectancies can alter the performance of children in a classroom (our 40 Studies
article “What You Expect Is What You Get”; this highlights the need to control experimenter bias
Surveys
large-scale and small-scale surveys—the scale of the survey is dependent on the number of surveys
collected, either a lot (large scale) or a few from a select group (small scale)
ex post facto studies take an effect and look back to determine the likely cause
use of Likert scale—a rating scale developed by R. Likert where respondents are asked to indicate
where they fall along some dimension; this is then converted into a numerical score (e.g. strongly
agree-1, agree-2, neither agree nor disagree-3, disagree-4, strongly disagree-5)
advantages include:
 flexibility in asking questions
 less time to collect data
 large amounts of data can be collected at once
disadvantages include:
 question-bias
 self-report bias
 erroneous memories of the subjects
 social desirability bias
Naturalistic Observation
participant observation—the observer is part of the group being observed
non-participant observation—the observer remains detached from the group; sometimes called a
complete observer
methods of recording data, including time, event and point sampling:
duration recording—the observer specifies the length of time a particular behavior will last (e.g.
talking to other student; being out of one’s set)
frequency-county method—counting the number of time (frequency) the behavior occurs
interval recording—a single subject is observed for a set amount of time and the subject’s behavior is
recorded
advantages of observations include:
 lessening self-report bias and social desirability
 information is not limited to what the subject can recall
disadvantages include:
 difficulty in measuring complex behavior
 expense
Descriptive Statistics
levels of measurement
 nominal scale—a unit of measurement using named categories such as eye color, gender,
voting status, etc.; no order and no indication of how groups differ are apparent; this is the
least refined of the four measurement scales; used frequently in non-participant
observations
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ordinal scale—a unit of measurement in which values to a variable can be rank ordered from
highest to lowest, such as class rank, percentile ranks, ordering ideas from best to worst, etc.
interval scale—a unit of measurement similar to ordinal scales but in which the difference
between each unit is equal or constant; the difference between 5 and 6 is the same as between
17 and 18
ratio scale—a unit of measurement based on ordinal and interval scales but comparisons can
be made using ratios; saying a number to two or three times greater than another number; this
is the most refined of the four measurement scales; used frequently in lab and field
experiments
measures of central tendency
mean—the average score from a group of scores
mode—the most frequent scores that occurs in a group of scores
median—the middle scores in a group of scores that separates the top half from the bottom
half from rank-ordered scores
measures of dispersion
 range—the difference between the highest and lowest score
 standard deviation—a numerical index that tells, on average, how far the scores fall from the
mean; the larger the standard deviation, the greater the spread of scores
 variance—the second moment around the mean; the expected value of the square of the
deviations of a random variable from its mean value
 quartile and semi-interquartile range—divides ranked data into four parts or quartiles
Inferential Statistics
probability—an estimation of how many times a certain event is likely to happen
levels of confidence—the level of certainty that an inferential statistic is not due to chance
 in experimental research .05 is the accepted minimum level of confidence
 in other words, there is less than a 5% chance that are results are in error
non-parametric tests—tests in which the results do not fall into a normal distribution
 chi-square test—a statistical procedure for use with nominal (frequency counts) and ordinal;
usually used in naturalistic observations
 Mann-Whitney U test—a test for use with two independent samples; the basis of this test is
that if all the data from the two samples are ranked, the high and low ranks should be evenly
distributed if the samples are equal; usually used in field or lab experiments
Graphical Techniques
bar chart—a graph using bars to denote numerical counts