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

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: Re: st: RE: AW: ratio function |

Date |
Sun, 25 Apr 2010 19:23:00 -0400 |

My previous example was flawed, Because males and females could be present in the same PSU (famid), the degrees of freedom for -suest- did not equal the sum of the d.f. for the separate regressions. Here is another example with proper strata. Note that the degrees now add properly. Steve ************************* webuse income, clear gen year = 2008 + (famid>68) tab year svyset famid, strata(year) svy: reg inc if year==2008 estimates store y2008 svy: reg inc if year==2009 estimates store y2009 suest y2008 y2009 matrix list e(V) //results from different years are independent nlcom _b[y2008:_cons]/_b[y2009:_cons] *********************************************** On Fri, Apr 23, 2010 at 10:40 AM, Steve Samuels <sjsamuels@gmail.com> wrote: > Just use -suest-. Use the fact that -reg- without an argument is > equivalent to estimating the mean. > > ******************** > webuse income, clear > svyset famid > svy: reg inc if male > estimates store Male > svy: reg inc if !male > estimates store Female > suest Male Female > nlcom _b[Male:_cons]/_b[Female:_cons] > ************************* > Steve > > 2010/4/23 Roman Kasal <kasal@trexima.cz>: >> yes, the year is another survey (different time; the years cannot be pooled because of degrees of freedom) and is included in strata. >> >> so there is no solution for this case? just manually? >> >> -----Original Message----- >> From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Steve Samuels >> Sent: Friday, April 23, 2010 1:32 PM >> To: statalist@hsphsun2.harvard.edu >> Subject: Re: Re: st: RE: AW: ratio function >> >>> "svy: mean wage, over(year)" is not equal "svy: mean wage if year==2009" >> >> The "if statement" is incorrect, unless year was a stratification >> variable that you identified to Stata. >> >> -nlcom- after -svy: mean-, over(year), is the proper approach. >> >> >> 2010/4/23 Roman Kasal <kasal@trexima.cz>: >>> ok, for this purpose I agree, that is ok...but what about if I want to calculate SE of Mean in years 2009 and 2008 and then ratio with SE of the means? >>> >>> the problem is that CI of >>> "svy: mean wage, over(year)" is not equal "svy: mean wage if year==2009" >>> for the year 2009 because of different degrees of freedom (SE's are equal), the first command gives wrong CI. >>> >>> is any elegant solution to handle this in Stata with "nlcom" or do I have to calculate it manually? >>> >>> thank you >>> >>> -----Original Message----- >>> From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Steve Samuels >>> Sent: Thursday, April 22, 2010 3:08 PM >>> To: statalist@hsphsun2.harvard.edu >>> Subject: Re: Re: st: RE: AW: ratio function >>> >>> The degrees of freedom are correct. See any sampling text. >>> >>> Briefly: To identify a subpopulation, each observation in the sample >>> receives a 0-1 indicator variable d. If X is the numerator variable >>> and Y is the denominator variable, the numerator for the ratio of is >>> the sum *over the entire sample* of Z_x = d *X and the denominator is >>> the sum of Z_y = d * Y. The standard errors are based on variability >>> in the Z's, including the zero values. >>> By the way, the standard errors formulas are valid only if the >>> expected number of observations in a subpopulation is at least 20. >>> >>> Steve >>> >>> 2010/4/22 Roman Kasal <kasal@trexima.cz>: >>>> thank you for the code, but I have found a problem: >>>> >>>> if I calculate over(foreign) the bound are enumerated with "e(N_psu)-e(N_strata)" degrees of freedom, but not for each foreign (degrees of freedom are for whole dataset) and this is wrong I assume. >>>> >>>> thank you >>>> >>>> -----Original Message----- >>>> From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Steve Samuels >>>> Sent: Friday, April 02, 2010 2:58 PM >>>> To: statalist@hsphsun2.harvard.edu >>>> Subject: Re: Re: st: RE: AW: ratio function >>>> >>>> Roman >>>> Perhaps we misunderstand what you are asking for. I We have been >>>> assuming that you want the ratio of the means of two variables >>>> ("columns"?) measured possibly on the same person. Perhaps you want >>>> the ratio of the means of one variable for two subpopulations. Both >>>> analyses will ignore missing values. >>>> >>>> If this is not what you desire, then please demonstrate by hand what >>>> you do want on a small, non-survey data set.. Also I'd like to know >>>> which R function does what are asking for >>>> >>>> The following do file computes the ratio of means with CI and then >>>> does the same for the log ratio and transforms to the original scale. >>>> >>>> -Steve >>>> >>>> >>>> **************************CODE BEGINS************************** >>>> capture program drop _all >>>> program antilog >>>> local lparm el(r(b),1,1) >>>> local se sqrt(el(r(V),1,1)) >>>> local bound invttail(e(df_r),.025)*`se' >>>> local parm exp(`lparm') >>>> local ll exp(`lparm' - `bound') >>>> local ul exp( `lparm' + `bound') >>>> di "parm =" `parm' " ll = " `ll' " ul = " `ul' >>>> end >>>> >>>> sysuse auto, clear >>>> svyset _n >>>> svy: mean mpg, over(foreign) >>>> nlcom (myratio1: _b[Domestic]/_b[Foreign]) //ratio >>>> nlcom (myratio2: log(_b[Domestic]/_b[Foreign])) // log ratio >>>> // Confidence interval of last -nlcom- on antilog scale >>>> antilog >>>> ***************************CODE ENDS*************************** >>>> >>>> >>>> >>>> . >>>> >>>> On Fri, Apr 2, 2010 at 2:37 AM, Roman Kasal <kasal@trexima.cz> wrote: >>>>> I don't agree...so how to do it when you want to find out ratio between >>>>> years, male X female, ...? So there is no solution? Just to keep N,mean, >>>>> SE, degrees of freedom, N_strata, N_psu, .... and calculate it manually? >>>>> I think it is not appropriate solution, at least to have it as an >>>>> option. I think there is missing a lot with complex survey in Stata and >>>>> complex survey is needed for almost every survey research, even freeware >>>>> R-project is better equipped :( >>>>> >>>>> so have a hope Stata will get it soon....immediately we are buying it >>>>> again :) >>>>> >>>>>> >>>>>> >>>>> And it should. Data (x,y) (1,2) (2,4) (3,6) (100,.) will give an >>>>> entirely different view of the data if the unpaired observation is >>>>> included in a mean or ratio calculation. Or consider data with x >>>>> missing in half the pairs and y missing in the other half; the ratio >>>>> of means would be meaningless. >>>>> >>>>> The formulas for standard errors for ratios assume that the data are >>>>> paired. Formally, they are based on the residual MSE of a regression >>>>> of y on x through the origin. You cannot do that regression with >>>>> unpaired data. >>>>> >>>>> If your concern is missing data, the solution is to impute the missing >>>>> values before analysis. >>>>> >>>>> Steve >>>>> >>>>> >>>>> * >>>>> * 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/ >>>>> >>>> >>>> >>>> >>>> -- >>>> Steven Samuels >>>> sjsamuels@gmail.com >>>> 18 Cantine's Island >>>> Saugerties NY 12477 >>>> USA >>>> Voice: 845-246-0774 >>>> Fax: 206-202-4783 >>>> >>>> * >>>> * 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/ >>>> >>> >>> >>> >>> -- >>> Steven Samuels >>> sjsamuels@gmail.com >>> 18 Cantine's Island >>> Saugerties NY 12477 >>> USA >>> Voice: 845-246-0774 >>> Fax: 206-202-4783 >>> >>> * >>> * 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/ >>> >> >> >> >> -- >> Steven Samuels >> sjsamuels@gmail.com >> 18 Cantine's Island >> Saugerties NY 12477 >> USA >> Voice: 845-246-0774 >> Fax: 206-202-4783 >> >> * >> * 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/ >> > > > > -- > Steven Samuels > sjsamuels@gmail.com > 18 Cantine's Island > Saugerties NY 12477 > USA > Voice: 845-246-0774 > Fax: 206-202-4783 > -- Steven Samuels sjsamuels@gmail.com 18 Cantine's Island Saugerties NY 12477 USA Voice: 845-246-0774 Fax: 206-202-4783 * * 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: Re: st: RE: AW: ratio function***From:*"Roman Kasal" <kasal@trexima.cz>

**References**:**Re: Re: st: RE: AW: ratio function***From:*"Roman Kasal" <kasal@trexima.cz>

**Re: Re: st: RE: AW: ratio function***From:*Steve Samuels <sjsamuels@gmail.com>

**RE: Re: st: RE: AW: ratio function***From:*"Roman Kasal" <kasal@trexima.cz>

**Re: Re: st: RE: AW: ratio function***From:*Steve Samuels <sjsamuels@gmail.com>

**RE: Re: st: RE: AW: ratio function***From:*"Roman Kasal" <kasal@trexima.cz>

**Re: Re: st: RE: AW: ratio function***From:*Steve Samuels <sjsamuels@gmail.com>

**RE: Re: st: RE: AW: ratio function***From:*"Roman Kasal" <kasal@trexima.cz>

**Re: Re: st: RE: AW: ratio function***From:*Steve Samuels <sjsamuels@gmail.com>

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