${\stackrel{\circledR }{\mathrm{x}}}_{\text{OC}}$	Mean value of the variable of interest in the OC sample
${\stackrel{\circledR }{\mathrm{x}}}_{\text{NOC}}$	Mean value of the variable of interest in the non‐OC sample
${\mathrm{n}}_{\text{OC}}$	OC sample size
${\mathrm{n}}_{\text{NOC}}$	non‐OC sample size
${\mathrm{s}}_{\text{OC}}^2$	Variance of the variable of interest in the OC sample
${\mathrm{s}}_{\text{NOC}}^2$	Variance of the variable of interest in the non‐OC sample