Simple imputation methods were inadequate for missing not at random (MNAR) quality of life data
Journal article, Peer reviewed
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http://hdl.handle.net/11250/2357192Utgivelsesdato
2008Metadata
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Sammendrag
Objective: QoL data were routinely collected in a randomised controlled trial (RCT), which
employed a reminder system, retrieving about 50% of data originally missing. The objective was to
use this unique feature to evaluate possible missingness mechanisms and to assess the accuracy of
simple imputation methods.
Methods: Those patients responding after reminder were regarded as providing missing
responses. A hypothesis test and a logistic regression approach were used to evaluate the
missingness mechanism. Simple imputation procedures were carried out on these missing scores
and the results compared to the actual observed scores.
Results: The hypothesis test and logistic regression approaches suggested the reminder data were
missing not at random (MNAR). Reminder-response data showed that simple imputation
procedures utilising information collected close to the point of imputation (last value carried
forward, next value carried backward and last-and-next), were the best methods in this setting.
However, although these methods were the best of the simple imputation procedures considered,
they were not sufficiently accurate to be confident of obtaining unbiased results under imputation.
Conclusion: The use of the reminder data enabled the conclusion of possible MNAR data.
Evaluating this mechanism was important in determining if imputation was useful. Simple imputation
was shown to be inadequate if MNAR are likely and alternative strategies should be considered.