Design of a frailty index among community living middle-aged and older people: The Rotterdam study.
OBJECTIVE
To design a frailty index (FI) and evaluate three methods to handle missing data. Furthermore, we evaluated its construct (i.e., skewed distribution, correlation with age and sub-maximum score) and criterion validity (based on mortality risk).


METHODS
We included 11,539 participants (45± years) from a population-based cohort in the Netherlands. Frailty was measured with a FI, which we constructed based on the accumulation of 45 health-related variables, related to mood, cognition, functional status, diseases and conditions, biomarkers, and nutritional status. A total FI-score was calculated by averaging the scores of the deficits, resulting in a score between 0 and 1, with higher scores indicating increasing frailty. Mean imputation, single- and multiple imputation were applied.


METHODS
Mortality data were obtained by notification from the municipal administration. Median follow-up time was 9.5 years, during which 3902 (34%) participants died.


RESULTS
The median FI for the full population was 0.16 (IQR=0.11-0.23). The distribution of the FI was slightly right-skewed, the absolute maximum score was 0.78 and there was a strong correlation with age (Pearson correlation=0.52;95%CI=0.51-0.54). The adjusted HR per unit increase in FI-score on mortality was 1.05 (95%CI=1.05-1.06). Multiple imputation seemed to provide more robust results than mean imputation.


CONCLUSIONS
Based on our results we advise to the use of at least 30 deficits from different health domains to construct a FI if data are not imputed. Future research should use the continuous nature of the FI to monitor trajectories in frailty and find preventive strategies.
Department of Epidemiology, Erasmus MC, Rotterdam, the Netherlands. Electronic address: j.schoufour@erasmusmc.nl.
Josje D
JD
Schoufour
Department of Epidemiology, Erasmus MC, Rotterdam, the Netherlands; Department of Biostatistics, Erasmus MC, Rotterdam, the Netherlands.
Nicole S
NS
Erler
Department of Epidemiology, Erasmus MC, Rotterdam, the Netherlands.
Loes
L
Jaspers
Department of Epidemiology, Erasmus MC, Rotterdam, the Netherlands; Leiden University College, The Hague,the Netherlands.
Jessica C
JC
Kiefte-de Jong
Department of Epidemiology, Erasmus MC, Rotterdam, the Netherlands.
Trudy
T
Voortman
Department of Epidemiology, Erasmus MC, Rotterdam, the Netherlands.
Gijsbertus
G
Ziere
Department of Clinical Chemistry, Erasmus MC, University Medical Center, Rotterdam, the Netherlands.
Jan
J
Lindemans
Department of Epidemiology, Erasmus MC, Rotterdam, the Netherlands; Department of Ophthalmology, Erasmus MC, Rotterdam, the Netherlands.
Caroline C
CC
Klaver
Department of Epidemiology, Erasmus MC, Rotterdam, the Netherlands.
Henning
H
Tiemeier
Department of Epidemiology, Erasmus MC, Rotterdam, the Netherlands.
Bruno
B
Stricker
Department of Epidemiology, Erasmus MC, Rotterdam, the Netherlands.
Arfan M
AM
Ikram
Division of Reproductive Medicine, Department of Obstetrics and Gynaecology, Erasmus MC, Rotterdam, the Netherlands.
Joop S E
JS
Laven
Department of Epidemiology, Erasmus MC, Rotterdam, the Netherlands; Department of Respiratory Medicine, Erasmus MC, Rotterdam, the Netherlands.
Guy G O
GG
Brusselle
Department of Epidemiology, Erasmus MC, Rotterdam, the Netherlands; Department of Internal Medicine, Erasmus MC, 3000 CA Rotterdam, the Netherlands.
Fernando
F
Rivadeneira
Department of Epidemiology, Erasmus MC, Rotterdam, the Netherlands.
Oscar H
OH
Franco
D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers; D005260:Female; D016330:Frail Elderly; D015577:Geriatric Assessment / Q000379:methods*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009026:Mortality; D009426:Netherlands
D015415:Biomarkers
Construct validity; Criterion validity; Frailty index; Missing data; Mortality