myCSG © |Area: ADaM| Concept: C1010 : ADaM BDS - Data Imputation | Lesson: L102 : LOCF-Records missing - using analysis visits-single parameter |

Background for LOCF
  • In clinical trials, we collect data at predetermined timepoints
  • These predetermined timepoints are called visits
  • Sometimes, the data could not be collected/reported at some visits for reasons like subject refused for a test or collected sample damaged etc
  • For analysis purposes, we may want to have all data available for each visit for all subjects
  • One approach to fill in the missing data is to assume that result would have been the same as previous available collection/result
  • This is technically called as 'last observation carried forward' and the newly 'filled' (created) record is called an imputed record/result
  • We fill in the missing visits with the results from the previous available result

ADaM implementation
  • CDISC ADaM standard allows for this kind of data imputation
  • As per the standard, we can create new derived records within the parameter
  • These new records have to be differentiated from the source records by populating the DTYPE variable
  • The value in DTYPE variable has to be 'LOCF' if we are using the 'last observation carried forward' approach
VARIABLE_NAMEVARIABLE_LABELDERIVATION
AVISIT Analysis Value SYSBP is collected every week from week 1 to week 5. For the subjects who do not have a result present in any analysis week from week 1 to week 5, create a new record for the missed analysis week by using the record which is closest to the missing analysis week.
DTYPE Derivation Type Set to 'LOCF' on the imputed record.
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