  The concept of blind analysis, a key procedure to remove the human-based
systematic error called confirmation bias, has long been an integral part of
data analysis in many research areas. In cosmology, blind analysis is recently
making its entrance, as the field progresses into a fully fledged
high-precision science. The credibility, reliability and robustness of results
from future sky-surveys will dramatically increase if the effect of
confirmation bias is kept under control by using an appropriate blinding
procedure. Here, we present a catalog-level blinding scheme for galaxy
clustering data apt to be used in future spectroscopic galaxy surveys. We shift
the individual galaxy positions along the line of sight based on 1) a geometric
shift mimicking the Alcock-Paczynski effect and 2) a perturbative shift akin to
redshift-space distortions. This procedure has several advantages. After
combining the two steps above, it is almost impossible to accidentally unblind.
The procedure induces a shift in cosmological parameters without changing the
galaxies' angular positions, hence without interfering with the effects of
angular systematics. Since the method is applied at catalog level, there is no
need to adopt several blinding schemes tuned to different summary statistics,
likelihood choices or types of analyses. By testing the method on mock catalogs
and the BOSS DR12 catalog we demonstrate its performance in blinding galaxy
clustering data for relevant cosmological parameters sensitive to the
background expansion rate and the growth rate of structures.
