We construct an updated extended compilation of distinct ( but possibly correlated ) f \sigma _ { 8 } ( z ) redshift space distortion ( RSD ) data published between 2006 and 2018 .
It consists of 63 data points and is significantly larger than previously used similar data sets .
After fiducial model correction we obtain the best fit \Omega _ { 0 m } - \sigma _ { 8 } \Lambda CDM parameters and show that they are at a 5 \sigma tension with the corresponding Planck15/ \Lambda CDM values .
Introducing a nontrivial covariance matrix correlating randomly 20 \% of the RSD data points has no significant effect on the above tension level .
We show that the tension disappears ( becomes less than 1 \sigma ) when a subsample of the 20 most recently published data is used .
A partial cause for this reduced tension is the fact that more recent data tend to probe higher redshifts ( with higher errorbars ) where there is degeneracy among different models due to matter domination .
Allowing for a nontrivial evolution of the effective Newton ’ s constant as G _ { \textrm { eff } } ( z ) / G _ { \textrm { N } } = 1 + g _ { a } \left ( \frac { z } { 1 + z } \right ) ^ { 2 } - g _ { a } % \left ( \frac { z } { 1 + z } \right ) ^ { 4 } ( g _ { a } is a parameter ) and fixing a Planck15/ \Lambda CDM background we find g _ { a } = -0.91 \pm 0.17 from the full f \sigma _ { 8 } data set while the 20 earliest and 20 latest data points imply g _ { a } = -1.28 ^ { +0.28 } _ { -0.26 } and g _ { a } = -0.43 ^ { +0.46 } _ { -0.41 } respectively .
Thus , the more recent f \sigma _ { 8 } data appear to favor GR in contrast to earlier data .
Finally , we show that the parametrization f \sigma _ { 8 } ( z ) = \lambda \sigma _ { 8 } \Omega ( z ) ^ { \gamma } / ( 1 + z ) ^ { \beta } provides an excellent fit to the solution of the growth equation for both GR ( g _ { a } = 0 ) and modified gravity ( g _ { a } \neq 0 ) .