Ch 5: Measurement Concepts

Reliability Reliability refers to the consistency or stability of a

measure of behavior [p92]

If you weighed yourself now and then at the end of class and you weighed the same both times, you would say the scale is reliable.

True score: The real score on the variable

Measurement error: occurs when a measure yields inconsistent results; the greater the inconsistency, the greater the measurement error

Reliability of Measures

How can we assess reliability?

• Correlation coefficients tell us how strongly two variables are related.

- Pearson Product-Moment Correlation Coefficient (noted as r in text) [p93]

Coefficients range from 0.00 to - 1.00 and 0.00 to +1.00

Sign of the coefficient indicates direction

Value of the coefficient indicates the strength

Reliability of Measures

- 1.00 + 1.000.00

Variables covary in opposite directions

Variables covary in the same direction

Methods of assessing reliability [pp 94-96]

Test-retest reliability: Assesses reliability of a score by measuring the same individuals at 2 points in time

Internal consistency reliability: Assesses reliability of the assessment tool (e.g. test) at one point in time Questions should yield consistent results Split-half reliability – individual’s total score on one half

of the test is correlated with the total score on the other half of the test

Methods of assessing reliability: Interobserver (Interrater) Reliability

A measure of how often two or more observers agree (are consistent) in their observations. [p96]

Nominal scale: percentage agreement

How we assess interobserver reliability:

Number of times two observers agree

____________________ X 100 Number of opportunities to agree

Construct Validity of Measures [pp 97-100]

Refers to the adequacy of the operational definition of variables

Is the measure that is used actually assessing what it is supposed to assess?

If so, it has face validity.

Example: Are facial expressions an adequate measure of happiness?

Indicators of construct validity

Face Validity: The content of the measure appears to reflect the construct being measured.

Content Validity: The content of the measure is linked to the universe of content that defines the construct• Facial expressions are part of a set of behaviors related

to happiness, such as body posture, thoughts, etc.)

Example: Are facial expressions an adequate measure of happiness?

Indicators of construct validity

Predictive Validity: Scores on the measure predict behavior on a criterion measured at a time in the future• SAT (Scholastic Aptitude Test predicts future success at

a university) Concurrent Validity: Scores on the measure are

related to a criterion measured at the same time• People who score high on a verbal anxiety test

experience increased sweating at the same time

• People who have happy facial expressions concurrently report feeling happy

Indicators of construct validity

Convergent Validity: Scores on the measure are related to other measures of the same construct.• A score for happy facial expression is related to a

score for body posture or mood or optimism Discriminant Validity: Scores on the measure

are not related to other measures that are theoretically different.• A score for happy facial expression is not related to

one for intelligence or cleanliness

Measurement Scales

Four levels for quantifying behavior: nominal, ordinal, interval, and ratio [p102-105]

Nominal scale

Classifies behaviors, events, and characteristics into different categories [p102]

No numerical or quantitative properties

Independent variables are often nominal or a categorical variable

OrdinalScale

Measurement scale in which events and behaviors can be rank ordered (i.e, first, second, third, etc.) [p103]

• Allows categories to be ordered first to last, highest to lowest, biggest to smallest, etc.

• Quantitative but no values attached to the intervals

Interval Scale

Measurement scale that allows researcher to specify how far apart two observations are on a given dimension [p104]

Difference between the numbers is meaningful• Intervals are equal in size

• Quantitative but no meaningful zero reference point

Ratio Scale

Measurement scale that is quantitative, with all numerical properties including an absolute zero reference point [p104]

Let’s practice! Identify the measurement scale for the following data:

Circle your marital status: Married Single Divorced Engaged

Let’s practice! Identify the measurement scale for the following data:

Circle your marital status: Married Single Divorced Engaged

NOMINAL

Let’s practice! Identify the measurement scale for the following data:

Do you go to work? Yes No

Let’s practice! Identify the measurement scale for the following data:

Do you go to work? Yes No

NOMINAL

Let’s practice! Identify the measurement scale for the following data:

If you work, how many hours a week do you work? _______

Let’s practice! Identify the measurement scale for the following data:

If you work, how many hours a week do you work? _______

RATIO

Let’s practice! Identify the measurement scale for the following data:

Rate your enjoyment of college on the scale below.

1 2 3 4 5

Not Very Much Very Much

Let’s practice! Identify the measurement scale for the following data:

Rate your enjoyment of college on the scale below.

1 2 3 4 5

Not Very Much Very Much

INTERVAL

Let’s practice! Identify the measurement scale for the following data:

What is your class standing?

Freshman Sophomore Junior Senior

Let’s practice! Identify the measurement scale for the following data:

What is your class standing?

Freshman Sophomore Junior Senior

ORDINAL