def METHOD_NAME(create_measured_data):
    df = create_measured_data(["WPR_DIFF_1"])
    df.remove_inactive_observations()
    assert all(
        df.data.columns.get_level_values("data_index").values == [400, 800, 1200, 1800]
    )
    assert all(
        df.data.columns.get_level_values("key_index").values == [400, 800, 1200, 1800]
    )