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Proc Surveyselect or the easy way to select samples

Proc Surveyselect or the easy way to select samples. Gitte Churlish Churlish Consulting. Sample selection (SAS 6). * to select 15 in a random fashion; Data temp; Set trees; select = ranuni (5432); run; Proc sort data = temp; by select; Data sample; set temp (obs = 15); run;.

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Proc Surveyselect or the easy way to select samples

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  1. Proc Surveyselect or the easy way to select samples Gitte Churlish Churlish Consulting

  2. Sample selection (SAS 6) * to select 15 in a random fashion; Data temp; Set trees; select = ranuni (5432); run; Proc sort data = temp; by select; Data sample; set temp (obs = 15); run;

  3. Proc Surveyselect Proc surveyselect data = trees Method = SRS n = 15 out = sample1; run; • Selects 15 samples from the population. • Sample1 – contains 15 records with sampling weights

  4. Methods • Simple random sample • Unrestricted random sample • Systematic random sample • Sequential random sample • PPS Sampling (7 methods)

  5. Use of strata Proc surveyselect data = trees Method = SRS n = 15 out = sample1; strata lv_d; run; • - select 15 trees from live, and 15 trees from the dead strata

  6. Sample size Proc surveyselect data = trees Method = SRS out = sample1; strata lv_d; Sampsize = 5,15; run; • select 5 trees from the dead strata and 15 trees from live • File must be sorted by strata variables

  7. Use of file for sample size procsurveyselect data=samp1 (where = (lv_d = 'L')) out=select_live method=sys seed = 5763 sampsize = no_to_select_live; strata age_grp spp_grp; Note use of SEED – provides repeatability

  8. Creation of sampsize file data no_to_select_live (keep = spp_grp age_grp _nsize_); set spp_grp_count_live; if age_grp = 'Mat' then do ; if spp_grp = 'BCHD-dec' then _nsize_ = 1; if spp_grp = 'BCHD-BL' then _nsize_ = 10; if spp_grp = 'BCHD-C' then _nsize_ = 1; if spp_grp = 'BCHD-HW' then _nsize_ = 3; if spp_grp = 'FPSL-FD-P' then _nsize_ = 11; if spp_grp = 'FPSL-LW' then _nsize_ = 3; if spp_grp = 'FPSL-S' then _nsize_ = 5; end ; if _nsize_ = 0 or _nsize_ = . then _nsize_ = 1; /* can't have a zero */ if _nsize_ > count then _nsize_ = count ; run;

  9. PPSWR sampling • Great for sampling in GIS files • Method = pps_wr • probability proportional to size and with replacement.

  10. PPS_WR example proc surveyselect data = GIS_polygon_file out = &file_out method = pps_wr outhits seed = &seed sampsize = samp_rate (rename = (max =_nsize_)); size polyarea; strata spec_cl vol_cls; run; NOTE: Size has been added, This indicates the variable to use for proportionality.

  11. Related Procs • Proc Surveyfreq • Proc surveymeans • Proc surveyreg • Proc surveylogistic • Take into account sampling weights

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