Chapter 8: Principles of Measurement

Question 1

What is measurement?

Answer 1

the process of assigning numerals to variables to represent quantities of characteristics according to certain rules

Question 2

What are the uses of measurement?

Answer 2

Describing quantity of an existing variable to determine its value.
Making decisions based on a criterion or standard of performance.
Drawing comparisons to choose between courses of action.
Evaluating responses to assess a patient’s condition by documenting change or progress.
Discriminating among individuals who present different profiles related to their conditions or characteristics.
Predicting outcomes to draw conclusions about relationships and consider expected responses.

Question 3

What are different types of variable measurements?

Answer 3

Dichotomous
Polytomous
Continuous
Discrete

Question 4

What are direct measures?

Answer 4

Direct observations of a physical property
Ex: range of motion in degrees or length in centimeters

Question 5

What are indirect measures?

Answer 5

For measures that are not observable, use an indirect or proxy measure
Ex: the height of a column of mercury to measure temperature

Question 6

What are constructs?

Answer 6

Abstract variables
Ex: intelligence, health, strength
Measured as some value assumed to represent the underlying variable
Measured according to expectations of how a person who possesses the specified trait would behave, look, or feel in certain situations.

Question 7

What are the levels of measurement?

Answer 7

Nominal
Ordinal
Interval
Ratio

Question 8

What is the nominal scale of measurement?

Answer 8

Classifications
No relative order
Numbers, letters or words may be used as category labels
- Blood type
- Gender
- Diagnosis
Arithmetic properties: counting (frequency)

Question 9

What is the ordinal scale of measurement?

Answer 9

Numbers indicate rank order
Intervals inconsistent or not known
Examples: manual muscle test, function, pain
Arithmetic properties: counts, percentages
- Medians useful for central tendency
- Cannot be added, subtracted, multiplied, or divided

Question 10

What is the interval scale of measurement?

Answer 10

Numbers indicate rank order and demonstrate equal intervals
No true zero
Ex: temperature in Fahrenheit or Celsius
Arithmetic properties: addition and subtraction

Question 11

What is the ratio scale of measurement?

Answer 11

Numbers indicate equal intervals and have a true zero
Ex: age, height, weight
Arithmetic properties: addition, subtraction, multiplication, and division

Question 12

What is the relevance of measurement scales?

Answer 12

Mathematical operations
Meaningful interpretations
Statistical procedures
- Parametric versus nonparametric tests

Question 13

What are dichotomous variables?

Answer 13

Numerals are used as labels, with no quantitative meaning, such as coding data on an opinion scale from “1” Strongly Disagree to “5” Strongly Agree. When the variable can take on only two values, such as using “0” to represent “No” and a “1” to represent “Yes” on a survey question, the measure is considered dichotomous.

Question 14

What are polytomous variables?

Answer 14

Variables that can have multiple values, such as a five-point opinion scale, are called polytomous.

Question 15

What is a continuous variable?

Answer 15

A continuous variable can theoretically take on any value along a continuum within a defined range.

Question 16

What is a discrete variable?

Answer 16

Some variables can be described only in whole integer units and are considered discrete variables. Heart rate, for example, is measured in beats per minute, not in fractions of a beat.