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Sources and handling of losses to follow-up in parallel-group randomized clinical trials in dogs and cats: 63 trials (2000-2005).

OBJECTIVE
To determine the sources and handlingof losses to follow-up (LTF) in parallel-group randomized clinical trials (RCTs).


SAMPLE POPULATION
63 parallel-group RCTs of > 24 hours' duration published from January 2000 through December 2005.


PROCEDURES
Journals were hand searched for eligible reports. Details concerning the presence, cause, and amount of LTF; statistical handlingof data missingbecause of LTF; type of analyses performed; number of animals randomly allocated and analyzed; and the acknowledgement of the potential impact of LTF were recorded. RESULTS In 81% (51/63) of trials, LTF were reported. In 80% (41/51) of those studies, losses in the analysis were ignored, and in only 18% (9/51) was the potential impact of LTF on study results acknowledged. Of the 47 studies in which sources of LTF were reported, 72% had loss of subjects because of investigator withdrawals, 30% because of deaths, and 26% because of owner withdrawals. Median loss of subjects for those studies was 12% because of investigator withdrawal (range, 2% to 52%), 8% because of death (1% to 28%), and 4% because of owner withdrawal (2% to 33%).


CONCLUSIONS AND CLINICAL RELEVANCE
Most RCTs had LTF, most of which were attributable to investigators removing randomly allocated animals from the study. In most studies, data from animal LTF were ignored and, therefore, only a subgroup of randomly allocated subjects was included in the data analysis. Most reports did not address the potential for a postrandomization selection bias associated with ignoring LTF and did not acknowledge the potential impact of the missingdata on their results.