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From |
jpitblado@stata.com (Jeff Pitblado, Stata Corp.) |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: matrices from svytab with col and se options |

Date |
Tue, 11 Jun 2002 09:45:20 -0500 |

Lee Sieswerda <Lee.Sieswerda@tbdhu.com> asks about the contents of -e(b)- and -e(V)- after -svytab-: > Its late in the day, so maybe I'm just tired, but -svytab- appears to be > acting strangely. If you run -svytab- with no options, a table is printed > with the cell proportions, and a corresponding vector e(b) is saved. If you > run -svytab- with the -col- option it prints the column proportions, but > e(b) still contains the regular cell proportions. This may not seem > exceedingly strange since it is easy enough to derive the column proportions > from the cell proportions for display purposes. However, if, in addition to > the -col- option, you also specify the -se- option (which prints the > standard errors in the table beneath the proportion estimates), then e(b) > contains the column proportions not the cell proportions. Is it just me, or > is that a little counter-intuitive? Wouldn't it be better to always return > the column proportions in e(b) when the -col- option is specified rather > than making it dependent on also specifying the -se- option? Also, > everything that I just said about the estimate vector e(b) applies equally > to the variance matrix e(V), which is even more sinister because its harder > to spot an error in the variance than in the estimate itself. -svytab- saves in e(setype) the type of variance (thus standard errors) that it returns in e(V). The default is -cell- proportions, unless you use the -se- option. If you want to work with the variances from the -column- proportions, then use the -column- and -se- options. Note that -e(V)- is the (co)-variance matrix of -e(b)-, thus if you are asking for the -column- proportion variances to be returned in -e(V)-, you are also asking for the -column- proportions themselves to be placed in -e(b)-. It is the variance (SE) calculations that specify what is put in -e(b)- and -e(V)- for -svytab-. ***** BEGIN . use auto . svytab for rep pweight: <none> Number of obs = 69 Strata: <one> Number of strata = 1 PSU: <observations> Number of PSUs = 69 Population size = 69 ---------------------------------------------------- | Repair Record 1978 Car type | 1 2 3 4 5 Total ----------+----------------------------------------- Domestic | .029 .1159 .3913 .1304 .029 .6957 Foreign | 0 0 .0435 .1304 .1304 .3043 | Total | .029 .1159 .4348 .2609 .1594 1 ---------------------------------------------------- Key: cell proportions Pearson: Uncorrected chi2(4) = 27.2640 Design-based F(4.00, 271.76) = 6.8334 P = 0.0000 . di e(setype) cell . mat li e(b) e(b)[1,10] p11 p12 p13 p14 p15 p21 y1 .02898551 .11594203 .39130435 .13043478 .02898551 0 p22 p23 p24 p25 y1 0 .04347826 .13043478 .13043478 . svytab for rep, col pweight: <none> Number of obs = 69 Strata: <one> Number of strata = 1 PSU: <observations> Number of PSUs = 69 Population size = 69 ---------------------------------------------------- | Repair Record 1978 Car type | 1 2 3 4 5 Total ----------+----------------------------------------- Domestic | 1 1 .9 .5 .1818 .6957 Foreign | 0 0 .1 .5 .8182 .3043 | Total | 1 1 1 1 1 1 ---------------------------------------------------- Key: column proportions Pearson: Uncorrected chi2(4) = 27.2640 Design-based F(4.00, 271.76) = 6.8334 P = 0.0000 . di e(setype) cell . mat li e(b) e(b)[1,10] p11 p12 p13 p14 p15 p21 y1 .02898551 .11594203 .39130435 .13043478 .02898551 0 p22 p23 p24 p25 y1 0 .04347826 .13043478 .13043478 . svytab for rep, col se pweight: <none> Number of obs = 69 Strata: <one> Number of strata = 1 PSU: <observations> Number of PSUs = 69 Population size = 69 ---------------------------------------------------------------- | Repair Record 1978 Car type | 1 2 3 4 5 Total ----------+----------------------------------------------------- Domestic | 1 1 .9 .5 .1818 .6957 | (0) (0) (.0552) (.1187) (.1171) (.0558) | Foreign | 0 0 .1 .5 .8182 .3043 | (0) (0) (.0552) (.1187) (.1171) (.0558) | Total | 1 1 1 1 1 1 | ---------------------------------------------------------------- Key: column proportions (standard errors of column proportions) Pearson: Uncorrected chi2(4) = 27.2640 Design-based F(4.00, 271.76) = 6.8334 P = 0.0000 . di e(setype) column . mat li e(b) e(b)[1,10] p11 p12 p13 p14 p15 p21 y1 1 1 .9 .5 .18181818 0 p22 p23 p24 p25 y1 0 .1 .5 .81818182 . qui log close ***** END --Jeff jpitblado@stata.com * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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