Variables and their Operational Definitions Measuring Variables

Introduction The basic requirements of all research in psychology is that a researcher must be able to measure the variables of interest. Objective versus subjective measures Structured versus unstructured measures Types of Variables Scales of Measurements Reliability Validity Operational Definition

Objective Versus Subjective It is traditional in psychology to differentiate between objective and subjective measures. The distinction is essentially between observations that all observers will agree about (objective measures) and those observations which are idiosyncratic to a particular observer and which are not shared by all observers (subjective measures) Example: Objective speed of reaction time to a signal the number of words correctly recalled Example: Subjective psychologists’ assessments of dangerousness of a sex offender

Structured versus Unstructured Research methods in psychology vary greatly in the degree of structuring involved. Structured highly structured methods are employed when there is a degree of clarity about the nature of the variables being measured and the likely range of different answers Unstructured unstructured methods are employed more when the psychologist is exploring issues that have not been widely researched before

Types of Variables The foundation of experiments are independent and dependent variables Independent Variables the condition that the researcher controls (manipulates) in order to test the variable’s effect on some outcome (dependent variable) Dependent Variables outcome variables of your research it is what the researcher is measuring or observing

Discrete/Categorical Types of Variables Variables Discrete/Categorical Continuous Ordinal Interval Ratio

Dichotomous Variables Types of Variables Dichotomous Variables variables that have only 2 categories e.g., yes or no Discrete Variables variables that increases and decreases by whole units e.g., 1, 2, 3 Continuous Variables variables that theoretically assume infinite number of values e.g., 1.2345, 2.23, 5.2458

Scales of Measurement Nominal Scale categorical; simple classification; identity; data consist of frequencies only a scale of measurement in which events are assigned to categories naming scales they represent categories where there is no basis ordering categories Examples eye color gender race

Scales of Measurement Ordinal Scale categories that can be ordered along a pre-established dimension but, no way of knowing how different the categories are from one another there are not equal intervals between the items arrangement of height (tall, normal short); winners in race (1st, 2nd, 3rd) Examples height: tall, medium, short winners: 1st, 2nd , 3rd

Scales of Measurement Interval Scale rank order with equal intervals; identity, magnitude & equal unit size permits rank ordering of events with the assumption of equal intervals between adjacent events Examples temperature: Fahrenheit & Celsius SAT tests: impossible to get zero IQ: impossible to have zero IQ

Scales of Measurement Ratio Scale rank order; equal interval; presence of a true zero point; identity, magnitude, equal unit size, absolute zero can make ratio comparisons “twice as much” or “3 times bigger” Examples height: 165 cm 5’6” weight: 65 kg 120 pounds amount of time to complete a task

Types of Measurement Self-report (behavioral, cognitive, affective) usually questionnaires or interviews the measure how people report that they act, think or feel Test (ability tests, personality) a measure instrument used to assess individual differences in various content areas Behavioral measures (counting behaviors, classifying behaviors) measures taken by carefully observing and recording behavior Physical measures (weight, pulse, blood measure, heart rate) measures of bodily activity

Variables and their Operational Definitions

Operational Definitions In order to conduct research and communicate meaningful with others, researchers must define the terms and concepts explicitly. For example, depression is defined conceptually as a state of being in which the individual exhibits initiative and has sad and gloomy thoughts. An operational definition specifies the observable and measurable characteristics of a term or concept. A researcher could define depression in terms of… Behavioral observations (e.g., affect level, content analysis of speech patterns) Survey (e.g., Beck Depression Inventory) Physiological measures (e.g., lateralization of EEG brain wave activity)

Operational Definitions An operational definition is a detailed specification of how one would go about measuring a given variable. Operational definitions should be tied to the theoretical constructs under study. The theory behind the research often claries the nature of the variables involved. Operational definition can range from very simple and straightforward to quite complex depending on the nature of the variable and the needs of the researcher. As researchers, we have to accept that there is no perfect operational definition for a given construct (e.g., IQ).