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Creating Valid and Effective Measures

Creating Valid and Effective Measures. Using –optifact- to Create Better Summated Rating Scales. North American Stata Users' Group Meetings Boston, July 11-12, 2005 . Are measures important?. Measures are how theory is translated into data for modeling

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Creating Valid and Effective Measures

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  1. Creating Valid and Effective Measures Using –optifact- to Create Better Summated Rating Scales North American Stata Users' Group Meetings Boston, July 11-12, 2005

  2. Are measures important? • Measures are how theory is translated into data for modeling • Unlike art, where we want to engage individual interpretation as a major component of the work • Measures need to be unambiguously interpreted in precisely the same way by all

  3. Why Scales? • Combining the results of several questions is more reliable and precise, and reduces measurement error (Spector, 1992)

  4. What makes a good scale? • It is reliable • The same measurement, produces similar results across time and persons • The questions or items that make up the scale are consistent with one another • It is valid • It measures the concept that it is intended to measure • It measures one concept • It is regularly distributed

  5. Reliability • Internal Reliability • Internal consistency: the items should inter-correlate (Cronbach’s Alpha) • Test-Retest Reliability • Same measure taken again should produce consistent results

  6. Validity • Rationale • The items must be consistent with theory and the concept under consideration • Criterion Validity • The items should vary in the same way to other variables that are theoretically related to the concept • Canonical correlation

  7. Uni-dimensional, Efficient • Scales that measure a single concept are more useful in establishing causal relationships • Efficient scales use only enough items to reliably measure a concept • Regular distributions allow standard modeling techniques

  8. Research Question • If my scales are not uni-dimensional, are there sub-scales which are and meet the criteria associated with good scales? • Investigated using data gathered for the Canadian National Longitudinal Survey of Children and Youth by Statistics Canada.

  9. Data and Method • The NLSCY cycles 1, 2 and 3 • Measures on parenting and child behaviour taken every two years (allows the investigations of test-retest reliability) N > 13,000. • Common factor analysis • Dimensions, alpha • Canonical correlation • Criterion validity

  10. Problems • There are a lot of candidate scales • 2k – 1, if scales of all sizes are considered • The testing procedure is lengthy • Factor analysis (dimensionality) • Alpha (internal reliability) • Canonical Correlation (external validity) • Re-test (all of the above, twice) • More than 13 scales

  11. Solution: optifact • A Stata software component to analyze a list of candidate items for the creation of a summated rating scale

  12. -optifact- Specification optifact varlist [weight] [if exp] [in range] [, top(#) smallest(#) largest(#) maxfact(#) minslope(#)] Varlist: the list of candidate items (numeric) Options: Top: the number of candidate scales to list (10) Smallest: the smallest k allowed (3) Largest: the smallest k allowed (all items) Maxfact: the maximum number of factors allowed (1)

  13. -optifact- Output optifact abecq6b abecq6n abecq6w abecq6p abecq6i abecq6qq abecq6hh abecq6s [aweight=awtcw01c], top(20) criteria(childsex ammcq01) 8 items will be processed There are 219 potential scales 56 combinations of 3 items had one factor, 0 had more than one factor Top 5 scales using 3 items Avg. Can K Alpha Cov. Chk Items - ----- ----- --- ----- 1 3 0.774 0.201 Yes abecq6p abecq6i abecq6qq 2 3 0.769 0.203 Yes abecq6p abecq6i abecq6hh 3 3 0.744 0.231 Yes abecq6b abecq6n abecq6hh 4 3 0.742 0.169 Yes abecq6p abecq6qq abecq6hh 5 3 0.734 0.213 Yes abecq6n abecq6p abecq6i 55 combinations of 4 items had one factor, 15 had more than one factor Top 5 scales using 4 items Avg. Can K Alpha Cov. Chk Items - ----- ----- --- ----- 1 4 0.802 0.185 Yes abecq6p abecq6i abecq6qq abecq6hh 2 4 0.784 0.199 Yes abecq6n abecq6p abecq6i abecq6hh 3 4 0.776 0.191 Yes abecq6n abecq6p abecq6i abecq6qq 4 4 0.775 0.198 Yes abecq6b abecq6p abecq6i abecq6hh 5 4 0.768 0.172 Yes abecq6p abecq6i abecq6qq abecq6s

  14. Behaviour Scales

  15. Parenting Scales

  16. Results • Of these 13 scales only one was uni-dimensional • Most had larger number of items than desirable for the value of alpha

  17. New Behaviour Scales

  18. New Parenting Scales

  19. Implications • These scales are part of a large survey conducted every 2 years in Canada on more than 20,000 children • The survey has completed 6 cycles of data collection • Each question has been asked more than 120,000 times

  20. Implications (Cont’d) • The scales required 85 questions • The revised scales require 30 questions • More than 55,000,000 questions

  21. Caveats • Most scales in the NLSCY are not the best that can be made from the available data • Some of these scales should not be used • The NLSCY is an excellent survey, conducted by competent statisticians • Similar results might be expected in other major surveys

  22. Conclusions • -optifact- can help find better measures • Uni-dimensional • Valid • Reliable • -optifact- can reduce costs • Equivalent or better measure for same money

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