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Measurement

Measurement

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Measurement

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  1. Measurement

  2. Measurement • The process whereby individual instances within a defined population are scored on an attribute according to rules • Usually given a numeric score • Measurement is meant to make comparisons among individual cases easier, more precise and more accurate

  3. Measurement • The easiest examples to understand involve the measurement of physical properties of objects • Height • Weight • Volume • Measuring intangibles such as opinion, intent, beliefs, etc. is difficult and open to error

  4. Measurement issues • Validity: does the measure actually reflect the underlying concept? • Are you measuring what you intend to measure? • Accuracy • Reliability: does the measure perform the consistently from one occasion to another? • Precision/sensitivity: how large are the differences between adjacent categories/scores? • Efficiency: cost versus value of information

  5. Self-report measures • Memory • Forgetting • Bias • Social desirability • Respondent may believe a given answer is more acceptable to the researcher • Knowledge • Respondents may not know or understand the ideas • Often, respondents will answer questions without really knowing what they are about

  6. Self-report measures • Sensitive to mood of the respondent • Sensitive to interview situation • Sensitive to data collection method • Internet • Interview • Paper and pencil

  7. Tests as measures • Pretty much all tests of your knowledge would fall under the category of self-report measures • All tests are prone to some level and type of error • Many types of tests exist, each having its strengths and weaknesses • Multiple-choice • Fill in the answer • Essay • Apply the concept

  8. The GRE • FairTest analysis • ETS analysis

  9. Observation • Internal states are only partially reflected in observable behavior, etc. • Behaviors are influenced by the situation, which may not be evaluated • May know they are being watched and change their behavior • Observer may engage in biased perception, interpretation, etc.

  10. Mechanical observation • Manifest behavior may not really reflect the underlying concept you think it does • Skin conductance • Website ‘hits’ • Often intrusive to the point of being unnerving • Eye tracking

  11. Eye Tracking Source: Max Planck Institute at: http://www.mpi.nl/world/tg/eye-tracking/eye-tracking.html

  12. Measurement levels • Differences in ‘measurement level’ refer to the kind of information conveyed in the scores individual objects receive • Four levels: nominal, ordinal, interval, ratio • More advanced levels provide a greater amount of information with the score they assign • More advanced levels allow for more powerful statistical analysis of the data

  13. Nominal-level measurement • Numbers are assigned to individual objects simply as a means to distinguish among them • Distinction without order

  14. A nominal-level measure 2 1 3 4 5 6

  15. Ordinal-level measurement • Scores indicate order, but not distance along some dimension • The difference between a one and a two may be greater or less than the difference between a two and a three

  16. An ordinal-level measure Large dog Score: 3 Small dog Score: 1 Medium size dog Score: 2

  17. Interval-level measurement • Scores indicate direction and distance • Intervals are of equal size—the difference between 1 and 2 is equal to the difference between 3 and 4 • The zero point is arbitrary—does not indicate complete absence of the attribute • Many statistical analyses assume this level of measurement

  18. An interval-level measure

  19. Ratio-level measurement • Scores indicate order and distance from a true zero point • The units along the scale are equal • Allows for calculation of the ratio of one point on the scale compared to another

  20. Ratio-level measures

  21. Scales • When measuring attitudes, behaviors, etc. there is bound to be a significant amount of measurement error • For reasons we will look at later, using multiple items/measures to create scores for individual objects improves the measurement of each one • We call measures combining multiple items to measure a single concept ‘scales’

  22. Scales • Each item in a scale is supposed to measure the construct of interest, but it is possible that either: • The concept has more than one dimension, or • The items tap into more than one concept • To test for multidimensionality, statistical techniques are available • Factor analysis • Interitem correlations

  23. Scale development • To improve the reliability/performance of the scale, a researcher may remove items that reduce reliability, etc. • May weight items according to their factor loadings

  24. Humor orientation scale Response categories: 1=strongly agree, 2=agree, 3=neutral, 4=disagree, 5=strongly disagree • I regularly tell jokes and funny stories when I am in a group • People usually laugh when I tell a joke or story • I have no memory for jokes or funny stories • I can be funny without having to rehearse a joke • Being funny is a natural communication style with me • I cannot tell a joke well • People seldom ask me to tell stories • My friends would say that I am a funny person • People don’t seem to pay close attention when I tell a joke • Even funny jokes seem flat when I tell them