private void CompareRegionalAgainstNational(GroupRoot groupRoot, IndicatorMetadata metadata)
        {
            if (comparer != null &&
                groupRoot.Grouping.Count > 1 &&
                CanCompareSubnationalAgainstNational(groupRoot.FirstGrouping.ComparatorMethodId))
            {
                Grouping regionalGrouping = groupRoot.GetSubnationalGrouping();
                Grouping nationalGrouping = groupRoot.GetNationalGrouping();

                if (nationalGrouping != null && regionalGrouping != null && regionalGrouping.ComparatorData != null)
                {
                    Significance significance = comparer.Compare(regionalGrouping.ComparatorData,
                        nationalGrouping.ComparatorData, metadata);
                    regionalGrouping.ComparatorData.AddSignificance(nationalGrouping.ComparatorId,
                        significance);
                }
            }
        }
        private static Grouping GetGrouping(IArea parentArea, GroupRoot groupRoot)
        {
            Grouping grouping = parentArea.IsCountry
                ? groupRoot.GetNationalGrouping()
                : groupRoot.GetSubnationalGrouping();

            if (grouping == null)
            {
                throw new FingertipsException(
                    "Cannot find both national and subnational groupings for indicator ID " +
                    groupRoot.IndicatorId + ". You may need to change the comparator for this indicator in FPM.");
            }
            return grouping;
        }