def turn_strat_into_label(stratum):
    """
    Convert age stratification string into a string that describes it more clearly.

    Args:
        stratum: String used in the model
    Returns:
        label: String that can be used in plotting
    """

    if 'up' in stratum:
        return stratum[4: -2] + ' and up'
    elif 'to' in stratum:
        to_index = stratum.find('to')
        return stratum[4: to_index] + ' to ' + stratum[to_index+2:]
    elif stratum == '':
        return 'All ages'
    else:
        return ''