Validity of the Katz Index to assess activities of daily living by informants in neuropathological studies

Ferretti-Rebustini, Renata Eloah de Lucena; Balbinotti, Marcos Alencar Abaide; Jacob-Filho, Wilson; Rebustini, Flávio; Suemoto, Claudia Kimie; Pasqualucci, Carlos Augusto Gonçalves; Farfel, José Marcelo; Leite, Renata Elaine Paraizo; Grinberg, Lea Tenenholz; Nitrini, Ricardo

doi:10.1590/S0080-623420150000600010

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ORIGINAL ARTICLE • Rev. esc. enferm. USP 49 (6) • Dec 2015 • https://doi.org/10.1590/S0080-623420150000600010 copy

Validity of the Katz Index to assess activities of daily living by informants in neuropathological studies

Validade do índice de katz para avaliar atividades básicas de vida diária por informantes em estudos neuropatológicos

Validez del índice de katz para evaluar las actividades básicas de vida diaria por informantes en estudios neuropatológicos

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

OBJECTIVE

To analyze the evidences of construct validity of the Katz Index for the retrospective assessment of activities of daily living (ADL) by informants, to assist neuropathological studies in the elderly.

METHOD

A cross-sectional study analyzed the functional ability of ADL measure by the Katz Index, of 650 cases randomly selected from the Brazilian Brain Bank of the Ageing Brain Study Group (BBBABSG) database. Sample was divided in two subsamples for the analysis (N=325, each) and then stratified according to cognitive decline assessed by the Clinical Dementia Rating Scale (CDR). Factor analyses with calculations of internal consistency and invariance were performed.

RESULTS

Factor analysis evidenced a unidimensional instrument with optimal internal consistency, in all subgroups. Goodness of fit indices were obtained after two treatments of covariance, indicating adequacy of the scale for assessing ADL by informants. The scale is invariant to cognitive decline meaning that it can be used for subjects with or without cognitive impairment.

CONCLUSION

Katz Index is valid for the retrospective assessment of basic ADL by informants, with optimal reliability.

Descriptors
Activities of Daily Living; Aging; Proxy; Psychometrics; Validation Studies

	Total	Subsample A	Subsample B
N	650	325	325
Gender Male [n(%)]	360 (55.4)	183 (56.3)	177 (54.5)
Female [n(%)]	290 (44.6)	142 (43.7)	148 (45.5)
Age (mean ± SD)	68.7 ± 11.3	69.2 ± 11.4	68.1 ± 11.2
Years of schooling (mean ± SD)	4.4 ± 3.5	3.891 ± 3.7	4.4 ± 3,4
IQCODE (mean ± SD)	3.2 ± 0.4	3.2 ± 0.5	3.1 ± 0.4
Katz Index (mean ± SD)	5.3 ± 1.7	5.3 ± 1.7	5.2 ± 1.8
Clinical Dementia Rating Scale [n(%)]
CDR 0	512 (78.8)	247 (76.0)	265 (81.5)
CDR 0.5	43 (6.6)	20 (6.2)	23 (7.1)
CDR 1	36 (5.5)	21 (6.5)	15 (4.6)
CDR 2	23 (3.5)	14 (4.3)	9 (2.8)
CDR 3	36 (5.5)	23 (7.1)	13 (4.0)

	Total	Without cognitive Impairment^* * Without cognitive impairment (CDR=0); With Cognitive impairment (CDR>0.5); (n=247)	With Cognitive Impairment^* * Without cognitive impairment (CDR=0); With Cognitive impairment (CDR>0.5); (n=78)
Gender Male/ Female (n)		152/ 95	31/ 47
Age (mean ± SD)		66.92 ± 10.68	76.52 ± 10.61
Years of schooling		4.19 ± 3.84	2.94 ± 2.99
IQCODE (mean ± SD)		3.0 ± 0.4	3.9 ± 0.6
Katz Index (mean ± SD)		5.8 ± 0.6	2.0 ± 3.5
Exploratory Factor Analysis
Range of item correlation	0.817 - 0.940	0.742 - 0.945	0.754 - 0.926
% of Correlations > 0.90	27	27	7
Determinant	9.674 ^-5	7.405 ^-5	0.001
KMO	0.918	0.880	0.905
X²Bartlett_(df)	2968.689 ₍₁₅₎^† † p<0.001 (X2Bartlett ).	2312.715 ₍₁₅₎^† † p<0.001 (X2Bartlett ).	558.412 ₍₁₅₎^† † p<0.001 (X2Bartlett ).
Communalities	0.822 - 0.950	0.721 - 0.975	0.777 - 0.916
Factors extracted	1	1	1
Eigenvalue > 1	1	1	1
1 ^stfactor	5.352	5.232	5.082
2 ^ndfactor	0.233	0.315	0.346
% variance explained by the 1^stfactor	87	85	82
Factor loadings	0.906 - 0.975	0.849 - 0.987	0.867 - 0.952

Reliability analysis
α-Cronbach (IC95% intraclass correlation)	0.974 (0.970 - 0.978)	0.966 (0.959 - 0.972)	0.964 (0.949 - 0.975)
Corrected Item-Total Correlation	0.892 - 0.958	0.835 - 0.966	0.863 - 0.934

	Katz Index (N=325)
Fitness Coefficients	Initial	Adjusted
X ²	39,21	4.32
Df	9	7
p -value	0.00	0.74
X ²_(df)	4.36	0.62
GFI	0.85	0.98
AGFI	0.65	0.95
NFI	0.93	0.99
TLI rho	0.91	1.00
CFI	0.95	1.00
SRMR	0.290	0.009
RMSEA (Confidence Interval 90%)	0.21 (0.14 - 0.28)	0.04 (0.00 - 1.01)
Number of Adjustments (errors controlled)	2	-

Universidade de São Paulo, Escola de Enfermagem Av. Dr. Enéas de Carvalho Aguiar, 419 , 05403-000 São Paulo - SP/ Brasil, Tel./Fax: (55 11) 3061-7553, - São Paulo - SP - Brazil
E-mail: reeusp@usp.br

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[1] Corresponding author: Renata Eloah de Lucena Ferretti-Rebustini. Av. Dr. Enéas de Carvalho Aguiar, 419 - Cerqueira César, CEP 05403-000 - São Paulo, SP, Brazil. reloah@usp.br

	Unconstrained	Fully Constrained	Difference	p -value	Invariance
Chi-square	297,467	305,481	8.014	0.155	Yes^* * Invariance assumed (groups are not different)
Df	13	23	5	0.155	Yes^* * Invariance assumed (groups are not different)
X ² /df (p -value)	16.526 (<0.001)	13.282 (<0.001)
CFI	0.902	0.901
RMSEA (IC90%)	0.219 (0.198 - 0.142)	0.195 (0.176 - 0.215)