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Measurement - PowerPoint PPT Presentation

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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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Experiment - effect of IV on DV

Independent variable 2 or more levels
Independent Variable (2 or more levels)


  • a) situational - features in the environment

  • b) task – type of task performed

  • c) instructional – type of instructions given

  • control vs experimental groups


  • 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 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


Categorical data

No quantitative information

E.g males and females


Ranked scores

Know relative position of scores

E.g affiliation ranking

Scales of measurement


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

  • Know relative difference between scores

  • E.g. IQ, temperature


  • Meaningful zero point.

  • Know absolute difference between scores.

  • E.g. height, reaction time


  • 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.


  • Are you measuring what you think you are measuring?

  • Validity assumes reliability

  • 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