Measurement and data quality
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Measurement and Data Quality. Measurement. The assignment of numbers to represent the amount of an attribute present in an object or person, using specific rules Advantages: Removes guesswork Provides precise information Less vague than words. Levels of Measurement.

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Measurement and Data Quality

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Measurement and data quality

Measurement and Data Quality


Measurement

Measurement

  • The assignment of numbers to represent the amount of an attribute present in an object or person, using specific rules

  • Advantages:

    • Removes guesswork

    • Provides precise information

    • Less vague than words


Levels of measurement

Levels of Measurement

  • There are four levels (classes) of measurement:

    • Nominal(assigning numbers to classify characteristics into categories) Gender, religion

    • Ordinal(ranking objects based on their relative standing on an attribute) "very dissatisfied," "somewhat dissatisfied," "somewhat satisfied," or "very satisfied."

    • Interval (objects ordered on a scale that has equal distances between points on the scale) Fahrenheit scale of temperature

    • Ratio (equal distances between score units; there is a rational, meaningful zero) amount of money you have in your pocket right now

  • A variable’s level of measurement determines what mathematic operations can be performed in a statistical analysis.


Errors of measurement

Errors of Measurement

  • Obtained Score = True score ± Error

    • Obtained score:An actual data value for a participant (e.g., anxiety scale score)

    • True score:The score that would be obtained with an infallible measure

    • Error:The error of measurement, caused by factors that distort measurement


Factors that contribute to errors of measurement

Factors That Contribute to Errors of Measurement

  • Situational contaminants

  • Transitory personal factors (e.g., fatigue)

  • Response-set biases

  • Administration variations

  • Item sampling


Question

Question

Is the following statement True or False?

  • The true score is data obtained from the actual research study.


Answer

Answer

  • False

    • The true score is the score that would be obtained with an infallible measure. The obtained score is an actual value (datum) for a participant.


Psychometric assessments

Psychometric Assessments

  • A psychometric assessmentis an evaluation of the quality of a measuring instrument.

  • Key criteria in a psychometric assessment:

    • Reliability

    • Validity


Reliability

Reliability

  • The consistency and accuracy with which an instrument measures the target attribute

  • Reliability assessments involve computing a reliability coefficient.

    • Reliability coefficients can range from .00 to 1.00.

    • Coefficients below .70 are considered unsatisfactory.

    • Coefficients of .80 or higher are desirable.


Three aspects of reliability can be evaluated

Three Aspects of Reliability Can Be Evaluated

  • Stability

  • Internal consistency

  • Equivalence


Stability

Stability

  • The extent to which scores are similar on two separate administrations of an instrument

  • Evaluated by test–retest reliability

    • Requires participants to complete the same instrument on two occasions

    • Appropriate for relatively enduring attributes (e.g., creativity)


Internal consistency

Internal Consistency

  • The extent to which all the items on an instrument are measuring the same unitary attribute

  • Evaluated by administering instrument on one occasion

  • Appropriate for most multi-item instruments

  • The most widely used approach to assessing reliability

  • Assessed by computing coefficient alpha (Cronbach’s alpha)

  • Alphas ≥.80 are highly desirable.


Question1

Question

When determining the reliability of a measurement tool, which value would indicate that the tool is most reliable?

  • 0.50

  • 0.70

  • 0.90

  • 1.10


Answer1

Answer

c. 0.90

  • Reliability coefficients can range from 0.0 to 1.00. Coefficients of 0.80 or higher are desirable. Thus, a coefficient of 0.90 would indicate that the tool is very reliable. A value greater than 1.00 for a coefficient would be an error.


Equivalence

Equivalence

  • The degree of similarity between alternative forms of an instrument or between multiple raters/observers using an instrument

  • Most relevant for structured observations

  • Assessed by comparing agreement between observations or ratings of two or more observers (interobserver/interrater reliability)


Reliability principles

Reliability Principles

  • Low reliability can undermine adequate testing of hypotheses.

  • Reliability estimates vary depending on procedure used to obtain them.

  • Reliability is lower in homogeneous than heterogeneous samples.

  • Reliability is lower in shorter than longer multi-item scales.


Validity

Validity

  • The degree to which an instrument measures what it is supposed to measure

  • Four aspects of validity:

    • Face validity

    • Content validity

    • Criterion-related validity

    • Construct validity


Face validity

Face Validity

  • Refers to whether the instrument looks as though it is an appropriate measure of the construct

  • Based on judgment; no objective criteria for assessment


Content validity

Content Validity

  • The degree to which an instrument has an adequate sample of items for the construct being measured

  • Evaluated by expert evaluation, often via a quantitative measure—the content validity index (CVI)


Question2

Question

Is the following statement True or False?

  • Face validity of an instrument is based on judgment.


Answer2

Answer

  • True

    • Face validity refers to whether the instrument looks like it is an appropriate measure of the construct. There are no objective criteria for assessment; it is based on judgment.


Criterion related validity

Criterion-Related Validity

  • The degree to which the instrument is related to an external criterion

  • Validity coefficient is calculated by analyzing the relationship between scores on the instrument and the criterion.

  • Two types:

  • Predictive validity: the instrument’s ability to distinguish people whose performance differs on a future criterion

  • Concurrent validity: the instrument’s ability to distinguish individuals who differ on a present criterion


Construct validity

Construct Validity

  • Concerned with these questions:

    • What is this instrument really measuring?

    • Does it adequately measure the construct of interest?


Some methods of assessing construct validity

Some Methods of Assessing Construct Validity

  • Known-groups technique

  • Testing relationships based on theoretical predictions

  • Factor analysis


Criteria for assessing screening diagnostic instruments

Criteria for Assessing Screening/Diagnostic Instruments

  • Sensitivity: the instruments’ ability to correctly identify a “case”—i.e., to diagnose a condition

  • Specificity: the instrument’s ability to correctly identify noncases, that is, to screen out those without the condition

  • Likelihood ratio: Summarizes the relationship between sensitivity and specificity in a single number

    • LR+: the ratio of true positives to false positives

    • LR-: the ratio of false negatives to true negatives


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