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


From   Mihir <mihir.statistics@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: Need help for chi-square test with survey command
Date   Wed, 30 Sep 2009 01:29:10 +0800

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 =      .

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