def METHOD_NAME(data_file: str) -> pd.DataFrame:
    """Load regional data from the original dataset.
    Note: This function does not standardize countries (since this is done later).
    Parameters
    ----------
    data_file : str or Path
        Path to original data file.
    Returns
    -------
    additional_combined_data : pd.DataFrame
        Regional data.
    """
    # Load regional data from original excel file.
    additional_data = pd.read_excel(data_file, sheet_name="Regional data", skiprows=1)[1:]
    # Prepare additional population data.
    population_columns = [
        "Region",
        "Western Europe.1",
        "Western Offshoots.1",
        "Eastern Europe.1",
        "Latin America.1",
        "Asia (South and South-East).1",
        "Asia (East).1",
        "Middle East.1",
        "Sub-Sahara Africa.1",
        "World",
    ]
    additional_population_data = additional_data[population_columns]
    additional_population_data.columns = [region.replace(".1", "") for region in additional_population_data.columns]
    additional_population_data = additional_population_data.melt(
        id_vars="Region", var_name="country", value_name="population"
    ).rename(columns={"Region": "year"})
    # Prepare additional GDP data.
    gdp_columns = [
        "Region",
        "Western Europe",
        "Eastern Europe",
        "Western Offshoots",
        "Latin America",
        "Asia (East)",
        "Asia (South and South-East)",
        "Middle East",
        "Sub-Sahara Africa",
        "World GDP pc",
    ]
    additional_gdp_data = additional_data[gdp_columns].rename(columns={"World GDP pc": "World"})
    additional_gdp_data = additional_gdp_data.melt(
        id_vars="Region", var_name="country", value_name=GDP_PER_CAPITA_COLUMN
    ).rename(columns={"Region": "year"})
    # Merge additional population and GDP data.
    additional_combined_data = pd.merge(
        additional_population_data,
        additional_gdp_data,
        on=["year", "country"],
        how="inner",
    )
    # Convert units.
    additional_combined_data["population"] = additional_combined_data["population"] * 1000
    # Create column for GDP.
    additional_combined_data[GDP_COLUMN] = (
        additional_combined_data[GDP_PER_CAPITA_COLUMN] * additional_combined_data["population"]
    )
    assert len(additional_combined_data) == len(additional_population_data)
    assert len(additional_combined_data) == len(additional_gdp_data)
    return additional_combined_data