def get_track_statistics_by_track_type(track, cohort_info_map):
    track_id = track[TRACK_ID_FIELD]

    result = {
        'samples': {
            'numberOf': get_number_of_unique_samples(track),
            'mutated_positions': get_number_of_mutated_positions(track)
        }
    }

    if track['type'] == 'tumor':
        cohort_info = cohort_info_map[track_id]
        result['cohort_size'] = cohort_info['size']
    else:
        # Do not assign cohort size for the 'COMBINED' track.
        result['cohort_size'] = None

    return result