690+reliability

Reliability -- and a couple of ways to “ensure” it.

From Fraenkel/Wallen website
 * []**

A reliable instrument is one that gives consistent results.


 * []**
 * The term "reliability," as used in research, refers to the consistency of scores or answers provided by an instrument.
 * Errors of measurement refer to variations in scores obtained by the same individuals on the same instrument.
 * The test-retest method of estimating reliability involves administering the same instrument twice to the same group of individuals after a certain time interval has elapsed.
 * The equivalent-forms method of estimating reliability involves administering two different, but equivalent, forms of an instrument to the same group of individuals at the same time.
 * The internal-consistency method of estimating reliability involves comparing responses to different sets of items that are part of an instrument.
 * Scoring agreement requires a demonstration that independent scorers can achieve satisfactory agreement in their scoring.

From Marcie's slides (wk 3)



From Fraenkel/Wallen ch. 7

reliablity: instrument gives consistent results

from ch. 8

reliability: consistency of scores obtained errors of measurement: variety of factors, variation by cc aka reliability coeffeicient (relationship betw scores of the same individuals on same instrument at 2 diff times or in two parts of same instrument.

three best ways to obtain a reliability coefficient: 1. test-retest method: same test twice to same group after certain interval has elapsed. effects of length of time, longer time then lower r.c. bc greter likelihood of changes to individual 2. equivalent-forms method: 2 different but equivalent (alternate/parallel) forms of instrument are admin. to same group during same time period; high rc shows that 2 forms are measuring the same thing 3. internal-consistency method: single admin of instrument slit-hal procedures: scoring 2 halves (like odds vs evens) separately for each person then calculating a cc for the 2 set scores using spearman-brown prophecy formula: alpha coeeficient: to check on interal consistency of instrument, aka cronback alpha

standard error of measurement (SEMeas): index shows extent in which measurement would vary under changed circumstances