Notice: On April 23, 2014, Statalist moved from an email list to a forum, based at statalist.org.

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

From |
Steven Samuels <sjsamuels@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: trying to compare means and using xi and xi3 for survey data |

Date |
Mon, 4 Jul 2011 23:34:47 -0500 |

I suspect a coding error. Suppose insure_cat is your original insurance variable. Have you looked at ******************************* bys insure_cat: sum totchg_num ***************************** Have you tabulated each insurance indicator against insure_cat? In any case, direct survey approaches are: ************************ svy: mean totchg_num, over(insure_cat) xi, noomit: svy: reg totch_num i.insure_cat, nocons //pre-Stata 11 svy: reg totch_num ibn.insure_cat, nocons //Stata 11 + ************************ Steve Steven J. Samuels Consultant in Statistics 18 Cantine's Island Saugerties, NY 12477 USA Voice: 845-246-0774 Fax: 206-202-4783 sjsamuels@gmail.com On Jul 4, 2011, at 5:02 PM, Hitesh Chandwani wrote: Hello Statalisters, I am using cost survey data and have 2 questions: 1) Comparison of means Using the svy: mean procedure, I can get means of cost for all categories of a particular variable. But since this variable is not dichotomous, using -test- or -lincom- as a postestimation command to compare the means, doesn't yield any results. What I thought of was dummy coding the categories and then running a regression. Instead of manually creating dummy variables, I decided to use -xi-; which brings me to my next question, 2) -xi- and -xi3- will both omit one category as a reference category..which is fine. But, in my output, after omitting the first category, another category is indicated as (dropped). Moreover, there is still no value for the F-statistic. Firstly, is my approach correct? And secondly, why are 2 categories being dropped? (One explanation that I could come up with for the 2 dropped categories is that the pweight for the observations in the omitted category " _Iinsured_p_0" is set to zero and hence Stata needs to use another category as reference) The following is my syntax as well as output: xi: svy: regress totchg_num i.insured_pub_pvt_un i.insured_pub~n _Iinsured_p_0-4 (naturally coded; _Iinsured_p_0 omitted) (running regress on estimation sample) Survey: Linear regression Number of strata = 75 Number of obs = 103817 Number of PSUs = 966 Population size = 469088.57 Design df = 891 F( 3, 889) = . Prob > F = . R-squared = 0.0106 ------------------------------------------------------------------------------ | Linearized totchg_num | Coef. Std. Err. t P>|t| [95% Conf. Interval] -------------+---------------------------------------------------------------- _Iinsured_~1 | 6504.334 915.0348 7.11 0.000 4708.46 8300.209 _Iinsured_~2 | (dropped) _Iinsured_~3 | -3015.988 705.0121 -4.28 0.000 -4399.666 -1632.31 _Iinsured_~4 | 1070.352 1961.327 0.55 0.585 -2779.007 4919.711 _cons | 13894.47 837.4082 16.59 0.000 12250.95 15538 ------------------------------------------------------------------------------ . test _Iinsured_p_1 _Iinsured_p_2 _Iinsured_p_3 _Iinsured_p_4 Adjusted Wald test ( 1) _Iinsured_p_1 = 0 ( 2) _Iinsured_p_2 = 0 ( 3) _Iinsured_p_3 = 0 ( 4) _Iinsured_p_4 = 0 Constraint 2 dropped F( 3, 889) = 23.78 Prob > F = 0.0000 Any help in understanding this issue will be greatly appreciated. Regards, -- Hitesh S. Chandwani University of Texas at Austin * * 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/ * * 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: trying to compare means and using xi and xi3 for survey data***From:*Hitesh Chandwani <hchandwani.stata@gmail.com>

**References**:**st: trying to compare means and using xi and xi3 for survey data***From:*Hitesh Chandwani <hchandwani.stata@gmail.com>

- Prev by Date:
**st: Re: mata in program define** - Next by Date:
**Re: st: Goodness of fit for discrete hazard model with unobserved heterogeneity** - Previous by thread:
**st: trying to compare means and using xi and xi3 for survey data** - Next by thread:
**Re: st: trying to compare means and using xi and xi3 for survey data** - Index(es):