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

VariablesAttributes

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

ValuesThe 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

RelationshipDoes a statistical relationship exist between the attributes of the variable?

The correspondence between two variables.

Types of Relationships

For ExampleYou 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 MeasuresAttributes 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 NOTEWe do not know the magnitude of the difference between the variables.

We just know there is a clear difference.

In Other WordsIf Middle Class is $30-50,000And Upper Class is $50,000+

Then The difference between the two could be pennies or millions of dollars – We don’t know.

Interval MeasuresThe 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 Scales5 = 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.

Good 1 2 3 4 5 6 7 BadRight 1 2 3 4 5 6 7 Wrong

Negative 7 6 5 4 3 2 1 Positive

Thurstone ScalesYES NO

People with AIDS are like my parents.

YES NOPeople with AIDS deserve what they got.

YES NOIt’s easy to get AIDS.

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 MeasuresThe 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.

ExampleIn 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 OrientationDV = Patient Satisfaction

Another ExampleWrench 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?

1) IV – Severity DV – Desired Information about Diagnosis

2) IV – Severity DV – Desired Information about Treatment

What were the IVs and DVs? Cont…

3) IV – Severity DV – Patient Compliance

Last ExampleIn a study by Wrench (2002), it was found that males were more physically and verbally aggressive than females.

What were the IVs and DVs?

1) IV – Sex (Males & Females) DV – Physical Aggression

2) IV – Sex (Males & Females) DV – Verbal Aggression