def dataframe_series_summary(series_summaries: dict) ->dict:
    """Aggregate certain statistics from the series summary

    Args:
        series_summaries: mapping from series to summary

    Returns:
        A aggregated summary based on the statistics of individual series
    """
    summary = {'na_count': 0, 'n_vars_missing': 0}
    for series_summary in series_summaries.values():
        if 'na_count' in series_summary and series_summary['na_count'] > 0:
            summary['na_count'] += series_summary['na_count']
    return summary
