NVR Inc. will join the S&P 500 index this month, the second change to the index announced this week. S&P Dow Jones Indices announced the change Friday afternoon, saying that the home-builder will replace Jefferies Financial Group Inc. in the index as of Sept. 26. Jefferies is moving down to the S&P MidCap 400 index after spinning off Spectrum Brand Holdings Inc. . Earlier in the week, S&P Dow Jones Indices announced that CDW Corp. will also move into the S&P 500 this month, replacing Total System Services Inc., which has been acquired. NVR shares declined 1.2% in after-hours trading Friday.