Measurement
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Measurement. Experiment - effect of IV on DV. Independent Variable (2 or more levels). MANIPULATED a) situational - features in the environment b) task – type of task performed c) instructional – type of instructions given control vs experimental groups NOT MANIPULATED

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Measurement

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Measurement

Measurement

Experiment - effect of IV on DV


Independent variable 2 or more levels

Independent Variable (2 or more levels)

  • MANIPULATED

  • a) situational - features in the environment

  • b) task – type of task performed

  • c) instructional – type of instructions given

  • control vs experimental groups

  • NOT MANIPULATED

  • Subject variable – existing differences of participants

  • - cannot infer causality because cannot manipulate

  • control vs comparison group


Dependent variable measured

Dependent Variable (measured)

  • The usefulness of the experiment depends on what is measured and how well you make the measurements

  • Uses operational definition


Measurement

  • Dependent variable defined operationally

  • Construct inferred from measure.

  • memory ; attention; social dominance; anxiety; aggression; work ethic; work load; bonding; helping behavior; hunger


Measurement type

Measurement type

  • Covert –gauges events that cannot be observed directly.

  • Empirical –based on directly observable events

  • Self-reported –based on feelings and perception of subject


Scales of measurement

Nominal

Categorical data

No quantitative information

E.g males and females

Ordinal

Ranked scores

Know relative position of scores

E.g affiliation ranking

Scales of measurement


Measurement

Interval

  • Constant separation between values of scale but no meaningful zero.

  • Know relative difference between scores

  • E.g. IQ, temperature

    Ratio

  • Meaningful zero point.

  • Know absolute difference between scores.

  • E.g. height, reaction time


Reliability

Reliability

  • Results are repeatable when measured again

  • No measure is 100% reliable (especially behavioral measure)

  • Measurement = True (hypothetical score) + measurement error

  • reliability most likely if use careful measurement procedure


Test retest reliability

Test-retest reliability

  • varies due to situational changes

  • sloppy measurement tool

  • assessed by correlation


Internal consistency reliability questionnaires

Internal consistency reliability: questionnaires

Measure each person one time but compare multiple answers

  • Split-half reliability : correlates the scores on one half of the test with the other half

  • Cronbach’s alpha : calculates the correlation of each item with every other item – alpha is the average of these correlation coefficients

  • Item-total : correlation of each item to the total score

  • (can assess individual questions too)


Inter rater reliability

Inter-rater reliability

  • The extent to which observers agree

  • Reliability tells us about measurement error but does not indicate if we are accurately measuring the variable of interest.


Validity

Validity

  • Are you measuring what you think you are measuring?

  • Validity assumes reliability


Measurement

  • Construct validity – is it a valid construct to measure and is the measuring instrument the best – ie adequacy of operational definition

  • Content/Face validity – common sense test

    does there seem to be a relationship between measure and construct

  • Criterion validity – judged by outcome


How good is the measure

How good is the measure?

  • predictive - does it accurately predict future behavior

  • convergent -is it meaningfully related to other measures of same thing

  • concurrent - people in groups known to differ on the construct differ on the measure

  • divergent (discriminant)- score on measure not related to other measure theoretically different


Measurement

  • If you have no reliability then your scores vary randomly and you cannot assess the impact of the IV

  • If you have no validity then your conclusions will be wrong.


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