private SurvivalData getSurvivalDataForPatient(int patientIndex, DataMatrix dataMatrix) {
    SurvivalData survivalData = new SurvivalData();

    survivalData.vitalStatus = getValue(patientIndex, VITAL_STATUS, dataMatrix);
    survivalData.daysToDeath = getValue(patientIndex, DAYS_TO_DEATH, dataMatrix);
    survivalData.lastFollowUp = getValue(patientIndex, LAST_FOLLOW_UP, dataMatrix);
    survivalData.lastKnownAlive = getValue(patientIndex, LAST_KNOWN_ALIVE, dataMatrix);

    return survivalData;
  }
  private SurvivalData mergeSurvivalData(SurvivalData sd1, SurvivalData sd2) {
    SurvivalData mergedSurvivalData = new SurvivalData();

    mergedSurvivalData.lastFollowUp = mergeWorksheetValues(sd1.lastFollowUp, sd2.lastFollowUp);
    mergedSurvivalData.lastKnownAlive =
        mergeWorksheetValues(sd1.lastKnownAlive, sd2.lastKnownAlive);
    mergedSurvivalData.vitalStatus = mergeWorksheetValues(sd1.vitalStatus, sd2.vitalStatus);
    mergedSurvivalData.daysToDeath = mergeWorksheetValues(sd1.daysToDeath, sd2.daysToDeath);

    return mergedSurvivalData;
  }