1. 1 Nonresponse adjustment A comparison between different estimators used in some Swedish surveys on rare items Jörgen Svensson Marina Jansson Statistics Sweden

2. 2 Horvitz-Thompson estimator  Simple estimator  Combined with straight expansion within strata  No auxiliary information  Excluding or including data from the nonresponse study

3. 3 Calibration for nonresponse estimator  Using auxiliary information  Excluding or including data from the nonresponse study  No weighting with data from the nonresponse study

4. 4 ”Two-phase” generalized regression estimator  Using auxiliary information  Excluding or including data from the nonresponse study  No weighting with data from the nonresponse study  Minor differences compared with calibration estimator

5. 5 Hansen-Hurwitz estimator  Subsampling the nonresponse ”stratum”  Weighting with data from this nonresponse study  No auxiliary information  Probably higher variance but lower nonresponse bias

6. 6 Hansen-Hurwitz estimator with calibration for nonresponse  Weighting with data from the nonresponse study  Using auxiliary information: totals for the nonresponse ”strata” totals for the population strata  Combination of two approaches for nonresponse treatment

7. 7 Results Farm Accidents Survey  A little fewer accidents, using Hansen-Hurwitz estimator: 3 700 → 3 500 farm accidents  (Measurement study gave larger effects)

8. 8 Results Pet Survey  Substantially fewer dogs, using Hansen-Hurwitz estimator: 810 000 → 730 000 dogs  A little fewer cats, using Hansen-Hurwitz estimator: 1.28 → 1.26 million cats

9. 9 Results Fishery Survey  Very much fewer fishing persons, using Hansen-Hurwitz estimator: 1.4 → 1.0 million persons  Very much fewer fishing days, using Hansen-Hurwitz estimator: 20 → 14 million days

10. 10 Results Fishery Tourism Survey  Survey with coverage problems and skewed population  Somewhat less turnover, using Hansen-Hurwitz estimator

11. 11 Conclusions  Hansen-Hurwitz is possible to combine with calibration!  Try to get high response rate in the nonresponse study!  To be considered when surveying rare items (phenomena correlated with response propensity) non-individuals with good chance of response