The basic ranking report uses a quartile ranking to display a range of coverage for employers. The range between the bottom and upper values represent the middle 50% of groups. If the value for the bottom is the same as the middle or even the upper it means that all groups in that range between the bottom and middle or upper have the same value.
Note, it does not mean that all groups in the entire range have equal coverage. There may be groups in the bottom 25%(below bottom) with even less or in the top 25%(above upper) with even more.
For more information please visit a related post in the community page.