Variable Lecture

An Introduction to the Use and Misuse of Research Variables “ A judicious man uses statistics, not to get knowledge, but to save himself from having ignorance foisted upon him.” --Thomas Carlyle

Variable Defined Any entity that can take on different values. Age is a variable because it can take different values for different people at different times.

Examples

Blood Pressure

Sex

Gender

Age

Extraversion

Patient Satisfaction

Heart rate

Political Party

Time

Weight

Height

Anxiety

Pleasure

Fear

Aggression

Attractiveness

The Aspects of Variables

Variables Attributes Values Relationship

1. Attributes The specific value of a variable.

Examples of Attributes

SEX

Male

Female

Gender

Assertive

Responsive

Androgynous

Math makes me anxious

Agree

Neutral

Disagree

Values The numerical aspect directly associated with a specific attribute.

Examples of Values

SEX

Male = 1

Female = 2

Gender

Assertive = 81< 120

Responsive = 0 < 40

Androgynous = 41<80

Math makes me anxious

Agree = 1

Neutral = 2

Disagree =3

Relationship Does a statistical relationship exist between the attributes of the variable? The correspondence between two variables.

Types of Relationships

For Example You do not become more female if your male level goes down. They are independent of each other. However, your level of assertiveness goes down as your responsiveness level goes up (negative relationship).

Levels of Measurement

Nominal Measures Attributes are only named. Also, referred to as categorical measures.

For Example

SEX

Male

Female

Ethnicity

Caucasian

African American

Middle Eastern

Indian

Native American

Other

Had a heart attack?

Yes

No

3 Characteristics of Nominal Variables 1. Must be mutually exclusive. 2. Must be equivalent. (no comparing apples to oranges) 3. Must be exhaustive.

What is the problem with this?

Republicans, Democrats, and Independents are not exhaustive of all possible political parties. How would you correct this? The simplest way would be to add an “other” category.

Ordinal Measures Attributes can be ordered.

For Example

SES

Lower Class

Middle Class

Upper Class

Education Level

Grade School

Middle School

High School

Junior College

College/University Graduate

Post Graduate

Letter Grade

A

B

C

D

F

BIG NOTE We do not know the magnitude of the difference between the variables. We just know there is a clear difference.

In Other Words If Middle Class is $30-50,000 And Upper Class is $50,000+ Then The difference between the two could be pennies or millions of dollars – We don’t know.

Interval Measures The distance between attributes has real quantitative meaning.

The distance between IQs of 80 & 100 is the same as the distance between IQs of 140 & 160.

However, we cannot say that someone with an IQ of 160 is twice as intelligent as someone with an IQ of 80. This would require an Absolute Zero.

General Examples

Patient Compliance

Temperature (Celsius and Fahrenheit)

Neuroticism

Extraversion

Patient Satisfaction

Physician Humor Orientation

Scaled Interval Measures - Likert - Semantic Differential - Thurstone

Likert Scales 5 = Strongly Agree; 4 = Agree; 3 = Undecided; 2 = Disagree; 1 = Strongly Disagree _____1. My physician regularly communicates with others joking with them. _____2. People usually do not laugh at my physician’s attempts at humor.

Semantic Differential Scales Numbers 1 and 7 indicate a very strong feeling. Numbers 2 and 6 indicate a strong feeling. Numbers 3 and 5 indicate a fairly weak feeling. Number 4 indicates you are undecided. Positive 7 6 5 4 3 2 1 Negative Wrong 1 2 3 4 5 6 7 Right Bad 1 2 3 4 5 6 7 Good

Thurstone Scales It’s easy to get AIDS. NO YES People with AIDS deserve what they got. NO YES People with AIDS are like my parents. NO YES

Important Scale Characteristics 1. Multiple questions measuring one concept. 2. Scales must be statistically reliable and valid. 3. Associated numerical values must be meaningful.

Ratio Measures The distance between attributes has real quantitative meaning, and has an absolute zero.

Celsius and Fahrenheit are Interval measures for temperature. Kelvin is a ratio measures for temperature because it has an absolute zero.

Examples

Temperature (Kelvin)

Age

Height

Weight

Mass

Blood Pressure

Speed

Heart Rate

Why Do Levels of Measurement Matter? The type of variables you have determine the statistical devices you can and cannot use.

See Picking a Test

Variables in Research

Dependent Variables The variable that is effected or not effected by another variable in a research study.

Independent Variables The variable that is being manipulated or examined in a study to see if it effects the dependent variable.

Example In a study by Wrench and Booth-Butterfield (2001), it was found that a physician’s humor orientation influenced her or his patient’s level of satisfaction.

What was the IV and DV? IV = Physician Humor Orientation DV = Patient Satisfaction

Another Example Wrench and Booth-Butterfield (2001) also found that the severity of a diagnosis influenced a patient’s desire for information about the diagnosis and information about treatment, but did not effect patient compliance.

What were the IVs and DVs?