Research Design and Statistics

Multiple Baseline Design

A single-subject design that involves sequentially applying a treatment to different "baselines" (e.g., to different behaviors, settings, or subjects). Useful when a reversal design would be impractical or unethical.

Hawthorne Effect

Refers to a change in performance resulting from participation in a research study (the novelty of the situation, increased attention, etc.).

Dependent Variable

The variable that is observed and measured in a research study and is believed to be affected in some way by the independent variable. In direct practice evaluation, the client's functioning is considered the dependent variable.

Cross-Sectional Studies

Studies conducted to assess the effects of aging and/or developmental changes over time (e.g., to assess the effects of age on IQ). Involves comparing groups of individuals representing different age groups or developmental levels at the same point in time. Cohort effects are a possible confound when conducting these studies.

Positively Skewed Distribution

A distribution in which scores are "piled up" in the negative (low score) side of the distribution, but a few scores are located in the distribution's positive tail.

External Validity

The degree to which a study's results can be generalized to other people, settings, conditions, etc.

Median

The measure of central tendency that is the middle score in a distribution of scores when scores have been ordered from lowest to highest.

Reactivity

The response of research subjects that is caused by their awareness of being participants in a research study and/or the knowledge that their behaviors are being observed. Can threaten a study's internal and external validity. Reactivity may also refer more generally to the tendency for people behave differently because they know they are being observed; this tendency can compromise the validity of a formal or informal observational procedure.

Ratio Scale

The scale of measurement that has equal intervals between successive points on the measurement scale and an absolute zero point. An absolute zero point makes it possible to multiply and divide ratio scores and to determine more precisely how much more or less of a characteristic one subject has compared to another.

Cross-Sequential Design

Used to assess the effects of aging and/or developmental changes over time. Combines cross-sectional and longitudinal methodologies by assessing members of two or more age groups at two or more different times.

Interval Scale

The scale of measurement that has equal intervals between successive points on the measurement scale. Most standardized educational and psychological tests provide scores that represent an interval scale. With an interval scale, the property of equal intervals allows you to perform the mathematical operations of addition and subtraction with the data.

Independent Variable

The variable that is manipulated in a research study for the purpose of determining its effects on the dependent variable. Also known as the experimental variable. In direct practice evaluation, the intervention is the independent variable.

Program Evaluation

In social work, assessments carried out to obtain information that can be used to improve social programs and social service accountability. Involves using applied social research to discover the extent to which social programs are carried out efficiently and effectively.

Mode

The measure of central tendency that represents the most frequently occurring category or score in a distribution.

Single-Subject Designs

Research designs that involve obtaining repeated measurements from a single subject over a specific period of time to measure changes in behaviors, attitudes, or beliefs. Each single-subject design includes at least one baseline (no treatment) phase and one treatment phase. As a result, the subject acts as their own no-treatment "control." In most single-subject designs, the dependent variable (behavior, attitude, or belief) is measured repeatedly at regular intervals throughout the baseline and treatment phases. If status on the dependent variable is stable within each phase of the study and changes only at the same time that the independent variable (treatment) is applied or removed, then it is likely that any observed change in the dependent variable is due to the effects of the independent variable rather than to history, maturation, or another extraneous factor.

Ordinal Scale

The scale of measurement in which the variable is divided into ordered categories, scores, or levels. A limitation of ordinal scores is that they do not lend themselves to determining just how much difference there is between scores. For example, we can't say that the person with a rank of 10 has twice as much of the characteristic as the person with a rank of 5, only that they are ranked higher.

Quasi-Experimental Research

Experimental research in which an investigator's experimental control is limited; especially their ability to assign subjects to groups because intact groups must be used, the variable of interest is an organismic variable, or the study includes only one group that will be compared to itself. A limitation of quasi-experimental research is that it does not allow an investigator to conclude that an observed relationship between variables is a causal one.

Analogue Studies

Studies conducted in a "facsimile of reality" (e.g., studies conducted in a laboratory or other artificial setting). A problem with analogue studies is that their results may have limited generalizability.

Internal Validity

The degree to which a research study allows an investigator to conclude that observed variability in a dependent variable is due to the independent variable rather than to other factors.

Case Studies

A general term used to describe an in-depth investigation of a single individual, family, organization, etc. A shortcoming is that their results might not be generalizable to other cases.

Ex-Post Facto Research

"After the fact" research in which the experimental treatment (independent variable) has been applied prior to the onset of the study. Because ex-post facto studies do not allow the experimenter to control the assignment of subjects to treatment groups, they are considered a type of quasi-experimental research.

Reversal (Withdrawal) Design

A type of single-subject design that includes, at a minimum, two baseline phases and one treatment phase (e.g., an ABA or ABAB design). The treatment is withdrawn ("reversed") during the second and subsequent baseline phases.

Nominal Scale

A scale of measurement in which the variable is divided into unordered groups or categories. When a variable is measured on a nominal scale (or is treated as though it were measured on a nominal scale), the data to be described or analyzed are frequency data (i.e., the frequency of observations in each group or category). The primary limitation of this measurement scale is that the only mathematical operation that can be performed on nominal data is to count the number (frequency) of cases in each category.

Arithmetic Mean

The measure of central tendency that is the arithmetic average of a set of scores. Can be used when scores are measured on an interval or ratio scale.

True Experimental Research

Experimental research that provides the investigator with maximal experimental control. Most important, when conducting a true experimental research study, an investigator can randomly assign subjects to groups, which makes it easier to determine if observed variability in the dependent variable was actually caused by the different levels of the independent variable.

Descriptive Research

Research conducted to describe behavior rather than to test hypotheses about behavior. Includes observational techniques, surveys and questionnaires, archival research, and case studies.

Scales of Measurement

The first consideration when choosing a statistical technique is usually the scale of measurement of the data that is to be described or analyzed. There are four different measurement scales - nominal, ordinal, interval, and ratio - and each involves dividing a set of observations into mutually exclusive and exhaustive categories. The differences between the four scales are that each provides a different kind of information and allows different mathematical operations to be performed.

Longitudinal Studies

Studies in which a group of subjects are followed and evaluated over an extended period of time in order to assess the effects of aging, natural developmental processes, or one or more other independent variable on one or more dependent variables over time.

Correlation Coefficient

A numerical index of the relationship (degree of association) between two or more variables. The magnitude of the coefficient indicates the strength of the relationship; its sign indicates the direction (positive or negative).

Demand Characteristics

Cues in an experimental situation that inform research participants of how they are expected to behave during the course of the study. Demand characteristics threaten a study's internal and external validity.

Cohort (Intergenerational) Effects

The effects of being part of a group (cohort) that was born at a particular time and, as a result, was exposed to unique educational, cultural, and other experiences. Cohort effects can confound the results of a cross-sectional study since any observed differences between age groups might be due to these effects rather than to differences in age only.