LECTURE 9

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MEASUREMENT

Procedure for assigning symbols, letters, or numbers to empirical properties of variables according to rules.

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Difficulty in measuring concepts directly (e.g., academic achievement)

Usually measure indicators of concepts (e.g., CGPA)

Level of measurement determines the type of statistical analysis.

The level of measurement you use depends on how you want to measure an outcome.

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LEVELS OF MEASUREMENT

Nominal Ordinal Interval Ratio

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NOMINAL Latin word nomin (name) Variable categorical in nature Differ in quality not quantity (numbers

have no meaning only label) Characterizes observation into one

(and only one) category mutually exclusive

Solely qualitative No obsolute zero (0) Matematical operation not possible.

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ORDINAL Describes variables that can be

ordered along some type of continuum.

Not only categories, order as well. Ranking according to various

outcomes, e.g., big & little. No obsolute ‘0’, only relative position;

e.g., Zul is taller than Sheereen and Sheereen is taller than Rozumah (no information on how much taller).

Matematical operation not possible.

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INTERVAL Latin word intervalum (spaces between

walls). Describes variables that have equal

intervals btw them. Allow us to determine the difference btw

points along the same type of continuum (e.g., the difference btw 300 and 400 is the same as the difference btw 700 and 800; i.e., 100).

0 is arbitrary (subjective, temporary). Simple matematical operation. More precise & convey > info than nominal

& ordinal; but must be cautious in interpreting.

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RATIO Latin word ratio (calculation). Describes variables that have equal

intervals btw them & have absolute 0. Most precise. Complex matematical operation. Highest level of measurement.

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QUIZ: MATCHING QUESTIONS

1.Nominal2.Ordinal3.Ratio4.Interval

A. Have a true zero (highest level).

B. Categorical in nature (lowest level)

C. Have equidistant points along some underlying continuum.

D. Are ranked.10

QUIZ: MATCHING QUESTIONS

1. Nominal2. Ordinal3. Ratio4. Interval

A. A is 5 inches taller than B (know precise difference).

B. Precise height measured on a scale with true zero.

C. Categorize people into A and B (people different in height).

d. Tall and Short (have some meaning, but nature of difference is not known).

TYPES OF MEASUREMENT ON HEIGHT

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SUMMARY

Nominal level variables are categorical in nature (lowest level)

Ordinal -- are ranked. Interval -- have equidistant points along

some underlying continuum. Ratio -- have a true zero (highest level).

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RELIABILITY & VALIDITY OF MEASUREMENT

Reliability and validity are the hallmarks of good measurement.

Assessments tools must be reliable and valid, otherwise the research hypothesis may be incorrectly rejected.

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Reliability is a practical measure of how consistent and stable a measurement instrument or a test might be.

Reliability is often measured using the correlation coefficient.

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SYNONYMS FOR RELIABILITY Dependency Consistency Stablility Trustworthiness Predictability Faithfulness

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TYPES OF RELIABILITY

1. Test-retest2. Parallel forms3. Inter-rater4. Internal consistency

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1. TEST-RETEST: A measure of stability. Examines consistency over time. Administer the same test/measure at

two different times to the same group of participants.

Coefficient: rtest1.test2

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2. PARALLEL FORMS A measure of equivalence. Examines consistency between forms. Administer different forms of the same

test to the same group of participants. Coefficient: rform1.form2

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3. INTER-RATER A measure of agreement. Examines consistency across raters. Have two raters, rate behaviors and

determine the amount of agreement between them.

Coefficient: % of agreement.

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4. INTERNAL CONSISTENCY A measure of consistently each item

measures the same underlying construct.

Examines reliability within a particular set of item.

Correlate performance on each item with overall performance across participants.

Coefficient: Chronbach’s alpha

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VALIDITY Is the quality of a test doing what it is

designed to do.

The test or instrument you are using actually measures what you need to have measured.

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SYNONYMS FOR VALIDITY

Truthfulness, Accuracy Authenticity Genuineness soundness

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TYPES OF VALIDITY

1. Content2. Criterion

i. Concurrentii. Predictive

3. Construct

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CONTENT VALIDITY

A measure of how well the items represent the entire universe of items

Established by asking expert if the items assess what you want them to.

History test = test items ask questions on history not Science.

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CRITERION VALIDITY

i. Concurrent validity A measure of how well a test

estimates a criterion.

Established by selecting a criterion and correlate scores on the test with scores on ther criterion in the present.

Good student = test result + reports by lecturers.

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ii. Predictive Validity A measure of how well a test predicts a

criterion.

Select a criterion and correlates scores on the test with scores on the criterion in the future.

High merit on STPM/Diploma = Score high CGPA.

Pass driving test = Good driver.

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CONSTRUCT VALIDITY A measure of how well a test assesses

some underlying construct.

Assess the underlying construct on which the test is based and correlate these scores with the scores.

Theoretically and practically sound.

Intelligence test actually measures intelligence.

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RELATIONSHIP BETWEEN RELIABILITY AND VALIDITY

A test can be reliable without being valid but the reverse is not true.A test can be reliable, but not valid, but a

test cannot be valid without first being reliable. Reliablity is a necessary, but not sufficient,

condition of validity. You are answering questions on simple addition,

but we called it spelling test! Obviously it is not a test on spelling lack of validity, does not affect reliability.

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