def disease_related(row):
    """
    Determine whether the cause of death was disease related or not from
    the value for Last Known Vital Status
    """
    last_vital = row.get("Last Known Vital Status", "Unknown") or "Unknown"

    if "deceased by disease" in last_vital.lower():
        ret = True
    elif "unknown" in last_vital.lower():
        ret = False
    else:
        ret = None

    return ret