sreg_ber                Semiparametric Model-Assisted Estimation under
                        a Bernoulli Sampling Design
sreg_pips               Semiparametric Model-Assisted Estimation under
                        a Proportional to Size Sampling Design
sreg_poisson            Semiparametric Model-Assisted Estimation under
                        a Poisson Sampling Design
sreg_srswr              Semiparametric Model-Assisted Estimation under
                        a Simple Random Sampling Without Replace
                        Sampling Design
sreg_stsi               Semiparametric Model-Assisted Estimation under
                        a Stratified Sampling with Simple Random
                        Sampling Without Replace in each stratum.
