Notice: On March 31, it was **announced** that Statalist is moving from an email list to a **forum**. The old list will shut down on April 23, and its replacement, **statalist.org** is already up and running.

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

From |
Stas Kolenikov <skolenik@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: GSAMPLE R3300 |

Date |
Thu, 6 Sep 2012 10:44:08 -0500 |

On Thu, Sep 6, 2012 at 9:28 AM, Lieke Boonen (SiRM) <Lieke.Boonen@sirm.nl> wrote: > We try to take a sample from our population, without replacement. we have several subgroeps with a high sampling weight. However with the gsample command it gives an error because for these cases the w_i*n /sum(w) is lager than 1. We thought the program looked at the relation between the weights and that this should not be a problem. Does anyone recognize this problem and is there a solution for this problem? As far as I can recall, -gsample- does a decent job of selecting one observation from the list, provided, as you found the hard way, that you don't have any certainty units. However, it is not appropriate for many real situation sampling problems, which usually require more complicated code. You also need to be aware that PPSWOR is a very non-trivial and counter-intuitive task. See http://www.citeulike.org/user/ctacmo/tag/unequal_prob_sampling for the appropriate references. All in all, you probably need to do this: 1. Identify the certainty units, set their probability of selection to 1. 2. Adjust the probability distribution, pulling up the probabilities for other units. 3. Check again for the certainty units: repeat steps 1-2 until the probability of selection on a single draw have converged. 4. Implement your PPS procedure -- systematic sample is the poor man, old days shortcut procedure to sample from the physical list on sheet(s) of paper that leads to technical difficulties in variance estimation; Rao-Hartley-Cochran is the easiest-to-implement shortcut that leads to an approximate PPS; Rao-Sampford used to be the most rigorous choice until Tille's elimination procedures appeared in the literature. -- -- Stas Kolenikov, PhD, PStat (SSC) :: http://stas.kolenikov.name -- Senior Survey Statistician, Abt SRBI :: work email kolenikovs at srbi dot com -- Opinions stated in this email are mine only, and do not reflect the position of my employer * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: GSAMPLE R3300***From:*Lucas <lucaselastic@gmail.com>

**References**:**st: GSAMPLE R3300***From:*"Lieke Boonen (SiRM)" <Lieke.Boonen@sirm.nl>

- Prev by Date:
**Re: st: Outreg margins error** - Next by Date:
**RE: st: Propensity Score Matching (PSM) - matching problem** - Previous by thread:
**Re: st: GSAMPLE R3300** - Next by thread:
**Re: st: GSAMPLE R3300** - Index(es):