Unit 2 Flashcards
Correlation Coeficient
r ± 1.0
-Sign indicates direction of association
-1.0 = Perfect, 0 = none
-.66 is considered high
-WK: Doesn’t imply causation
-STR: Predicts bhvr
Scatterplot
Graphic rep. of corr.
- = Units
-Visual that shows direction & magnitude of corr.
-Helps find outliars
Pearson’s Corr (P’s r)
Most used corr. measure
-Used w/ linear corr. & cont. data
Spearman’s Rho
Corr. calculated w/ rank-order data
-If rank between variables is similar, STR + corr.
Restricted Rng
Scores are tightly clustered
-DEC corr. b/c easiness to move btwn ranks
-DEC variability
Regression
“Line of best fit” (regression line) makes predictions using corr. btwn 2 Vs
-Residual (Diff. btwn observed & predicted scores) stays at MIN
-STR of corr. = INC accuracy in predictions, DEC in error
-Observe 1 group and make predictions for another
-Tendency to overestimate relationship
Standard Error of Est.
Gives margin info of error when estimating
Coefficient of Determinism (CoD)
Coefficient^2
Coefficient of Alienation
Measures non-associations btwn Vs
-Square root of 1 - CoD
Shrinkage
Amount of DEC observed when
regression is applied to another group
Reliability
Consistency of scores
-Degree matters
-Key psychometric feat.
Rel. Coefficient
Corr. coefficient indicates rel.
Rel. (R) Tests
-Test-restest R.
-Alternate / Parallel forms R.
-Split-half / INT Consistency R.
-Inter-rater R.
Classical Test Theory
x = T + e
-x = Obt. score
-T = true score
-e = Random error
EI True score plus random error = obtained score
Systematic (NOT random) Error
Error effecting variability
Variance
Difference in scores from error & differences in ability
Sources of e (random error) in test scores
Test administration
-Test-taker Vs, ENVI & administer-related factors
Test construction
-Items used, item sampling/selection
Test scoring & interpretation
Different test = diff. e
Measurement of e & R
e DEC R & repeatability of psych test
Classical Theory
Unsystematic measurement e randomly influences
-Measurement e is random
-M e = 0
-True scores and e are not corr., rTe = 0
- e on different tests are not corr., r 12 = 0
Reliability & Classical T
True score / Total variance
-Total variance = True score + e variance
-0 (coefficient) = Diff. due to e or chance
-1 = true difference
-0 or 1 = improbable
Test-restest Method
1 test given to 2 pple on 2 different occasions
-Shows corr. btwn 1st & 2nd scores for the same test
-H corr = stable test / has test-retest R.
-L corr. = Random e OR No rel., no stability
Things to Consider w/ Test-retest R.
Time btwn testing
-Usually days-wks pending on V. Is expected to change
-Rapid changing V = needs sm btwn time, otherwise person changed
How much time is appropriate?
-Ability tests: Time needed to wear off practice & mem. effects
-practice effect = problem for academic & neuropsych settings
Test-retest = best when practice effects don’t affect/minimal
Alt./Parallel Reliability (Coefficient of Equivalence) Method
Two versions (V.a, V.b) of test given to 1 group of pple
-Group takes both tests
-V.b can be given immediately or w/ delay after V.a
Alt./Parallel Rel. Cont.
Corr. btwn V.a & V.b = Having similar qualities/concepts
Corr. btwn V.a & V.b = concepts diff.
-Maybe caused by item sampling or wording
-Use blueprint to prevent L corr.
STR & WK of Alt./Parallel R.
STR:
-DEC cheating/memory effect b/c subjects get different items w/ different form
*Practice effect possible b/c items on different forms are similar
WK:
-INC time, money, & effort to create new version of same test
Internal Consistency Reliability
Inter-corr. of items in same test
-Tests w/ heterogeneous items usually have low INT Consistency Rel.
INT consistency Rel. Method
1 test given to 1 group on 1 occasion
-Test is split in half, subtotal for each half are corr.
-Best: Odd-even, randomly, matched items
-Worst: 1st & 2nd half
Split-half
Yields corr. btwn two half tests, NOT rel. of full test
-Is longer w/ good quality
-More rel. than shorter tests b/c it fully samples bhvr
*Is pic rel. to someone’s appearance VS many pics?