Introduction to Research Design
Transcript Introduction to Research Design
Purpose of this Section of the Research Support Lab
Purpose of This RSL Part:
• Make statistics fun!
• Make you into a statistician!
• Introduce you to basic concepts and procedures in descriptive and inferential
• Prepare you for subsequent statistical courses
Overview of These RSL Parts:
• Begins with methods for describing and summarizing single-variable
(frequency) distributions followed by methods for describing relationships
between two (or more) variables.
• Then introduce probability theory as background for understanding
• Methods are then presented for drawing inferences from research samples to
populations from which the samples were drawn.
• Statistical tests covered include z-tests, t-tests, analysis of variance
(F-tests), and nonparametric tests
Shavelson, R.J. (1996). Statistical reasoning for the behavioral
sciences (3rd Ed.). Boston: Allyn & Bacon.
• Supplemental Material
Ruiz-Primo, M.A., Mitchell, M., & Shavelson, R.J. (1996).
Student guide for Shavelson statistical reasoning for the
behavioral sciences (3rd Ed.). Boston: Allyn & Bacon.
• Research is doing one’s damnedest to answer perplexing
• Or research is a systematic approach to finding answers to
• Scientific research, our focus, seeks answers to questions
empirically and by inference, ruling out counter-interpretations
to the one justified by the data
• With the scientific method, problems are formulated,
hypotheses are identified, data are collected, inferences are
drawn about which hypothesis is more credible
• The purpose of empirical research, therefore, is to provide
answers to questions about behavior using the scientific method
• Statistics is the science of conducting studies to collect, organize,
summarize, analyze, and draw conclusions from data.
• Descriptive statistics consists of:
presentation of data
• Inferential statistics consists of:
generalizing from samples to populations
determining relationships among variables
Research Questions/Steps in Conducting Research
• What is happening?
• Is there a systematic (causal) effect?
• Why or how is it happening (“mechanism”)?
Steps in Conducting Research
Identify and define a research problem
Formulate hypothesis based on theory, research, or both
Design the research
Conduct the research
Analyze the data
Interpret the data as they bear on the research question
Data Collection and Sampling Techniques
• Surveys are the most common method of collecting data. Three
methods of surveying are:
– Telephone surveys
– Mailed questionnaire surveys
– Personal interviews
• Other methods include historical data gathering (empirical data)
Variable: is a characteristic or attribute that can assume different values(height,
Data are the values that variables can assume.
Random variables have values that are determined by chance.
A population consists of all subjects that are being studied.
A sample is a group of subjects selected from a population.
Random samples are selected using chance methods or random methods.
Independent Variable(Factor/Treatment): A variable that is measured , manipulated
(type of instruction), or selected (e.g., sex) to determine its relationship to some other
Control Variable: A variable which is held constant (or is “controlled”) to neutralize its
effect on the dependent variable because it is not the focus of the study (e.g., control
on sex in a reading study)
Intervening Variable: A conceptual or theoretical variable that accounts for the
relation between independent and dependent variable; an explanation for the
relation or a hypothesized mechanism that accounts for the relation.
Dependent Variable(Response): A variable that is observed and measured to
determine its response to the independent variable (i.e., dependent on the
• Nominal—classifies data into mutually exclusive (nonoverlapping), exhausting categories in which no order or ranking
can be imposed on the data.
• Ordinal—classifies data into categories that can be ranked;
however, precise differences between the ranks do not exist.
• Interval—ranks data, and precise differences between units of
measure do exist; however, there is no meaningful zero.
• Ratio—possesses all the characteristics of interval measurement,
and there exists a true zero.
Measurement Scales: Classification of Data
Some Terminology: Summation Notation
Summation notation is mathematical notation commonly
used in statistics
It’s really simple if you pause, take a deep breath, relax and
enjoy it… a little patience goes a long ways
Mean X X p / N ( X 1 X 2 ... X p ... X N ) / N
• Pre-experimental Designs
– One-shot Case Study (Treatment group only)
– One Group Pretest to Posttest Design—measures of change
– Intact Group Comparison at posttest
• Experimental Designs
Random assignment to “treatment” & control group
– Posttest Only Control Group
– Pretest-Posttest Control Group
• Quasi-experimental Designs
Non-random assignment to “treatment” & control group observed
– Nonequivalent-Control Group Design
– Time-Series Design
• Ex-Post Facto Designs
Statistical controls for comparing alternative “treatments”
– Correlational Design
– Criterion-Group Design
• One-shot Case Study (Treatment group only)
“X” is a new personnel policy, a job satisfaction measurement is taken, and then a response is observed
• One Group Pretest to Posttest Design—measures change
A job satisfaction measurement is taken before and after treatment “X” is applied
• Intact Group Comparison at posttest
G1 receives the treatment, G2 does not; then a job satisfaction measurement is taken and observed
(in this case G1 and G2 may represent two different business units)
Random assignment to “treatment” & control group
• Posttest Only Control Group
• Pretest-Posttest Control Group
A job satisfaction measurement is taken after treatment “X1” is applied or not and graveyard shift
“X2” is implemented
Non-random assignment to “treatment” & control group observed.
Include one or more control groups.
• Nonequivalent-Control Group Design
Subjects receive a pretest (O1) treatment or non-treatment and then receive a posttest (O2)
• Time-Series Design
Multiple observations are taken before and after a treatment is administered. Pretreatment
observations establish a control group baseline. Post-treatment observations establish a consistent
change in response.
Ex-Post Facto Designs
Statistical controls for comparing “treatment” and “control”
(relationships between two variables). Called ex-facto because the
researcher arrives after the treatment has been administered.
SAT scores (O1) and GPA (O2) are collected.
Group 2 is compared to Group 1
Threats to Internal Validity
- something co-occurring with the treatment caused the outcome
- maturation, not the treatment, caused the outcome
- loss of poorly performing subjects from a group caused the outcome
• Statistical Regression
- extreme groups are likely to improve on retesting
• Selection bias
- the differences in outcomes existed before the treatments were given
- outcome measure not reliable, valid, or both
- pretest cued subjects to outcome measure
- Type I Error
Occurrence of events other
than the independent variable.
There may be developmental
(physical or mental) changes
occurring to the subjects during the
time of the experiment
Some subjects drop out
the study and they have
something in common,
say, low achievement.
The groups were selected on the basis
of extreme score. (Regression effect:
low-extreme tends to increase, highextreme tends to drop)
exist in groups
The measuring instruments is not reliable
or not valid, therefore, the score obtained
by subjects could not be accurate.
The subject learns from the pretest,
therefore, scores better on the
Do not reject
A type I error occurs if one rejects the null hypothesis when it is true.
A type II error occurs if one does not reject the null hypothesis when it is false.
(Control Group + Random Assignment)
Select two out of the four major Research Designs.
Support your two selected research designs with original
hypothetical examples as outlined in this presentation.
Compare and contrast them with one another.
Indicate all threads to validity that you can document.