By adopting the differential age method, we utilize selected 17832 luminous red galaxies (LRGs) from Sloan Digital Sky Survey Data Release Seven (SDSS DR7) covering redshift 0<z<0. 4 to measure Hubble parameters. Using a full spectrum fitting package UlySS, these spectra are reduced with single stellar population (SSP) models and optimal age information of our selected sample are derived. With the decreasing age-redshift relation, four new observational H (z) data (OHD) points are obtained, which are H (z) =69. 019. 6 km s^-1 Mpc^-1 at z=0. 07, H (z) =68. 626. 2 km s^-1 Mpc^-1 at z=0. 12, H (z) =72. 929. 6 km s^-1 Mpc^-1 at z=0. 2 and H (z) =88. 836. 6 km s^-1 Mpc^-1 at z=0. 28, respectively. Combined with other 21 available OHD data points, a performance of constraint on both flat and non-flat CDM model is presented.
Zhang et al. (2014) studied this question.