PT  - JOURNAL ARTICLE
AU  - Denis Mongin
AU  - Kim Lauper
AU  - Carl Turesson
AU  - Merete Lund Hetland
AU  - Eirik Klami Kristianslund
AU  - Tore K Kvien
AU  - Maria Jose Santos
AU  - Karel Pavelka
AU  - Florenzo Iannone
AU  - Axel Finckh
AU  - Delphine Sophie Courvoisier
TI  - Imputing missing data of function and disease activity in rheumatoid arthritis registers: what is the best technique?
AID  - 10.1136/rmdopen-2019-000994
DP  - 2019 Oct 01
TA  - RMD Open
PG  - e000994
VI  - 5
IP  - 2
4099  - http://rmdopen.bmj.com/content/5/2/e000994.short
4100  - http://rmdopen.bmj.com/content/5/2/e000994.full
SO  - RMD Open2019 Oct 01; 5
AB  - Objective To compare several methods of missing data imputation for function (Health Assessment Questionnaire) and for disease activity (Disease Activity Score-28 and Clinical Disease Activity Index) in rheumatoid arthritis (RA) patients.Methods One thousand RA patients from observational cohort studies with complete data for function and disease activity at baseline, 6, 12 and 24 months were selected to conduct a simulation study. Values were deleted at random or following a predicted attrition bias. Three types of imputation were performed: (1) methods imputing forward in time (last observation carried forward; linear forward extrapolation); (2) methods considering data both forward and backward in time (nearest available observation—NAO; linear extrapolation; polynomial extrapolation); and (3) methods using multi-individual models (linear mixed effects cubic regression—LME3; multiple imputation by chained equation—MICE). The performance of each estimation method was assessed using the difference between the mean outcome value, the remission and low disease activity rates after imputation of the missing values and the true value.Results When imputing missing baseline values, all methods underestimated equally the true value, but LME3 and MICE correctly estimated remission and low disease activity rates. When imputing missing follow-up values at 6, 12, or 24 months, NAO provided the least biassed estimate of the mean disease activity and corresponding remission rate. These results were not affected by the presence of attrition bias.Conclusion When imputing function and disease activity in large registers of active RA patients, researchers can consider the use of a simple method such as NAO for missing follow-up data, and the use of mixed-effects regression or multiple imputation for baseline data.