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Re: st: Need help for chi-square test with survey command


From   Mihir <mihir.statistics@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Need help for chi-square test with survey command
Date   Sat, 3 Oct 2009 17:48:00 +0800

Many thanks Stas.

On Thu, Oct 1, 2009 at 10:07 PM, Stas Kolenikov <skolenik@gmail.com> wrote:
>
> Stata uses Rao-Scott corrections for the scale and degrees of freedom
> of the independence test chi^2. It might have happened that something
> went negative because of this corrections. For instance, in your
> extended case, you lost 1.02 degrees of freedom to the design (compare
> chi2(9) and F(7.98, something) ).
>
> On Thu, Oct 1, 2009 at 8:19 AM, Mihir <mihir.statistics@gmail.com> wrote:
> > Dear all:
> >
> > Anybody has any idea what can be done in the case below?
> >
> > Thanking you,
> > Mihir
> >
> > On Wed, Sep 30, 2009 at 1:29 AM, Mihir <mihir.statistics@gmail.com> wrote:
> >>
> >> Dear all:
> >>
> >> I am stuck with a problem in pearson chi-square test with survey
> >> command. I have setup survey setting for Nationwide Inpatient Survey
> >> (NIS) data. I used hospital id as sampling unit, discwt as sampling
> >> weight and stratum variable as strata as suggested on NIS website.
> >> When I am trying to run chi-square test for independence between age
> >> category and year of data collection from 1998 to 2007, it gives
> >> proper result, but when I run the same command by retaining only two
> >> years (1998 and 2007), it does not produce p-value. I don't understand
> >> why it is happening? Can anybody help me - what I should do? I am also
> >> getting similar results with other variables that same command works
> >> with more year but doesn't work with two years.
> >>
> >> I have pasted my output for your ready reference.
> >>
> >> Thanking you in advance,
> >> Mihir
> >>
> >> svyset hospid [pweight=discwt], strata(stratum) vce(linearized)
> >>
> >>      pweight: discwt
> >>          VCE: linearized
> >>     Strata 1: stratum
> >>         SU 1: hospid
> >>        FPC 1: <zero>
> >>
> >> svy: tabulate year age2cat, count column row obs percent format(%10.0g) pearson
> >> (running tabulate on estimation sample)
> >>
> >> Number of strata   =        60                  Number of obs      =    157222
> >> Number of PSUs     =      3270                  Population size    = 759816.12
> >>                                                Design df          =      3210
> >>
> >> -------------------------------------------
> >>          |             age2cat
> >>     YEAR |  <65 year   >=65 yea      Total
> >> ----------+--------------------------------
> >>     1998 | 27548.394  10497.654  38046.048
> >>          | 72.408029  27.591971        100
> >>          | 4.9658285  5.1193873  5.0072705
> >>          |      5452       2102       7554
> >>          |
> >>     1999 | 25591.467  9586.1825  35177.649
> >>          | 72.749224  27.250776        100
> >>          |  4.613076  4.6748901  4.6297582
> >>          |      5265       1991       7256
> >>          |
> >>     2000 |  25067.72  9839.9109  34907.631
> >>          | 71.811576  28.188424        100
> >>          | 4.5186663  4.7986258  4.5942209
> >>          |      5163       2032       7195
> >>          |
> >>     2001 | 24673.646  9882.7968  34556.443
> >>          | 71.401001  28.598999        100
> >>          | 4.4476311  4.8195399  4.5480007
> >>          |      4983       1976       6959
> >>          |
> >>     2002 | 83751.067  30869.413  114620.48
> >>          | 73.068152  26.931848        100
> >>          | 15.096831  15.054075  15.085292
> >>          |     17682       6513      24195
> >>          |
> >>     2003 | 80686.437  27375.013  108061.45
> >>          |  74.66718   25.33282        100
> >>          | 14.544405  13.349963  14.222053
> >>          |     17002       5737      22739
> >>          |
> >>     2004 | 77406.999  26898.738  104305.74
> >>          | 74.211641  25.788359        100
> >>          | 13.953259  13.117698   13.72776
> >>          |     16052       5540      21592
> >>          |
> >>     2005 | 74552.231  27032.143  101584.37
> >>          | 73.389467  26.610533        100
> >>          | 13.438663  13.182755    13.3696
> >>          |     15263       5507      20770
> >>          |
> >>     2006 | 68720.522  26875.807  95596.329
> >>          | 71.886152  28.113848        100
> >>          | 12.387449  13.106515  12.581508
> >>          |     14234       5538      19772
> >>          |
> >>     2007 | 66760.785  26199.193  92959.979
> >>          | 71.816696  28.183304        100
> >>          |  12.03419  12.776551  12.234536
> >>          |     13813       5377      19190
> >>          |
> >>    Total | 554759.27  205056.85  759816.12
> >>          | 73.012306  26.987694        100
> >>          |       100        100        100
> >>          |    114909      42313     157222
> >> -------------------------------------------
> >>  Key:  weighted counts
> >>        row percentages
> >>        column percentages
> >>        number of observations
> >>
> >>  Pearson:
> >>    Uncorrected   chi2(9)         =   91.4953
> >>    Design-based  F(7.98, 25611.84)=    3.0966    P = 0.0017
> >>
> >> keep if year==1998|year==2007
> >>
> >> svy: tabulate year age2cat, count column row obs percent format(%10.0g) pearson
> >> (running tabulate on estimation sample)
> >>
> >> Number of strata   =        60                  Number of obs      =     26744
> >> Number of PSUs     =      1205                  Population size    = 131006.03
> >>                                                 Design df          =      1145
> >>
> >> -------------------------------------------
> >>           |             age2cat
> >>      YEAR |  <65 year   >=65 yea      Total
> >> ----------+--------------------------------
> >>      1998 | 27548.394  10497.654  38046.048
> >>           | 72.408029  27.591971        100
> >>           | 29.210724   28.60642  29.041449
> >>           |      5452       2102       7554
> >>           |
> >>      2007 | 66760.785  26199.193  92959.979
> >>           | 71.816696  28.183304        100
> >>           | 70.789276   71.39358  70.958551
> >>           |     13813       5377      19190
> >>           |
> >>     Total | 94309.179  36696.848  131006.03
> >>           | 71.988428  28.011572        100
> >>           |       100        100        100
> >>           |     19265       7479      26744
> >> -------------------------------------------
> >>   Key:  weighted counts
> >>         row percentages
> >>         column percentages
> >>         number of observations
> >>
> >>
> >>   Pearson:
> >>     Uncorrected   chi2(1)         =    0.9557
> >>     Design-based  F(., .)         =         .     P =      .
> >>
> >> *
> >> *   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/
> >
>
>
>
> --
> Stas Kolenikov, also found at http://stas.kolenikov.name
> Small print: I use this email account for mailing lists only.
>
> *
> *   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/

*
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