Fraction of the C iv-enriched H i absorber number density to the total absorber number density as a function of redshift. The left panel is derived from the Δv_C iv = ±100 km s^-1 sample, while the right panel represents the Δv_C iv = ±10 km s^-1 sample. The black open circles represent a column density interval of log  N_H i = [12.75,14.0] and the filled circles represent log  N_H i = [14,17]. The vertical error bars mark 1σ Poisson errors, while the x-axis error bars show the redshift range covered by each sightline. In the left panel for log  N_H i = [12.75,14.0] (gray open circles), two lowest data points at log  (1 + z) ~ 0.5 (or z ~ 2) including an upper limit are from Q1101−264 and Q0122−380. Both have a short redshift coverage, therefore become more susceptible to cosmic variance. Sightlines with no C iv-enriched H i absorbers are plotted as upper limits with an arbitrary value of 0.05 and 0.002 for log  N_H i = [14,17] and log  N_H i = [12.75,14.0], respectively.