Understanding health measurement scales (ch 12)

what is a summative scale ?

-total score is obtained by ADDING values across a set of items

-items on the scale are generally on and ORDINAL scale

-all items contribute equally to the total score

-types of formats may include: LIKERT scales, VISUAL ANALOG scales

what is a cumulative scale ?

-items reflect increasing severity of the characteristic being measured

-each item is DICHOTOMOUS

-total cumulative score based on the number of items the individual agrees with

-max score is the number of items

-diff individuals w same score should have the same level of ability

-aka: GUTTMAN scales

what is a scale ?

-an ordered system based on a series of Qs or items, resulting in a score that represents the degree to which respondent possess a particular latent trait (attitude, value, characteristic)

-should be unidimensional, representing a single construct

-generic or related to specific patient groups

describe characteristics of a Likert scale

-ORDINAL SCALE (disagree to agree)

-range from low to high
(odd number (1-5), with neutral point)
(even number 1-6 forces choice)

discuss the application and limitations of visual analog scales in clinical practice

-fixed at 100mm (10cm) in length
(measured in mm but underlying measure is ordinal)

-anchors at extremes
(best to worst)

-frequently used to measure intensity of pain from a patients perspective

-also used to measure other constructs: stress, anxiety, disability, fatigue, quality of life

variations of visual analog series

-numeric rating scale
(ex: rating pain from 0-10)
(ordinal scale)

-face rating scale
(ex: use of different faces to represent aspects of pain)
(developed for use in children but may be used with adults)

describe the role of Rasch analysis for understanding cumulative scales

-based on item response theory
(ranking of persons, hierarchy of items)

-uses: transformation of ordinal data into interval values, translation of scores across instruments (ability level of respondent and difficulty of items are the same across instruments)

-questionnaire items expected to fit a model whereby item difficulty and person ability are consistent

-differential item functioning (DIF)
(item bias in the fit to Rasch model for different groups (cultures, disorders, age)

computer adaptive testing

-based on item response theory

-designed to adjust the difficulty of items to match ability of test taker

-used for standardized testing

-can be used to reduce the # of items administered with a health status questionnaire