poisson modelling

[Masoumeh Sanagou]

Hi Statalist,

I used following data to do poisson modelling:

Year M_all_P M_G_High_L1_AUse_RR15_C_adj M_all_L1_AUse_RR15_C_adj
1987 5520001 211.9177 501.407
1988 5633569 216.2777 511.7229
1989 5755082 221.1636 523.2832
1990 5867299 225.8139 534.2859
1991 5973605 230.4786 545.3229
1992 6074767 234.9648 555.9374
1993 6155299 239.3794 566.3824
1994 6236709 243.6229 576.4227
1995 6325682 250.3768 592.4029
1996 6417271 260.5307 616.4274
1997 6502261 273.0925 646.1493
1998 6581291 282.8546 669.2469
1999 6664289 289.1082 684.043
2000 6749964 298.3964 706.0193
2001 6847125 313.2063 741.0602
2002 6952335 336.035 795.0741
2003 7057470 350.3287 828.8935
2004 7158720 364.5615 862.5689
2005 7269239 382.8875 905.9291
2006 7391066 400.3706 947.295
2007 7547610 415.8048 983.8129
2008 7724059 429.8253 1016.986
2009 7915795 440.6469 1042.59
2010 8064259 448.9114 1062.145
2011 8199360 456.432 1079.939
2012 8356709 465.1911 1100.663
2013 5792143 322.43 762.8839

. poisson M_all_L1_AUse_RR15_C_adj Year, exposure(M_all_P)
note: you are responsible for interpretation of noncount dep. variable

Iteration 0:   log likelihood = -127.10332
Iteration 1:   log likelihood = -127.10331

Poisson regression                              Number of obs     =         27
                                                LR chi2(1)        =     431.15
                                                Prob > chi2       =     0.0000
Log likelihood = -127.10331                     Pseudo R2         =     0.6291

------------------------------------------------------------------------------------------
M_all_L1_AUse_RR15_C_adj |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------------------+----------------------------------------------------------------
                    Year |   .0191066   .0009262    20.63   0.000     .0172912     .020922
                   _cons |  -47.34115   1.854261   -25.53   0.000    -50.97544   -43.70687
             ln(M_all_P) |          1  (exposure)
------------------------------------------------------------------------------------------

. poisson M_G_High_L1_AUse_RR15_C_adj Year , exposure(M_all_P)
note: you are responsible for interpretation of noncount dep. variable

Iteration 0:   log likelihood = -107.80178
Iteration 1:   log likelihood = -107.80178

Poisson regression                              Number of obs     =         27
                                                LR chi2(1)        =     182.22
                                                Prob > chi2       =     0.0000
Log likelihood = -107.80178                     Pseudo R2         =     0.4580

---------------------------------------------------------------------------------------------
M_G_High_L1_AUse_RR15_C_adj |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
----------------------------+----------------------------------------------------------------
                       Year |   .0191066   .0014247    13.41   0.000     .0163142    .0218991
                      _cons |  -48.20238   2.852216   -16.90   0.000    -53.79262   -42.61214
                ln(M_all_P) |          1  (exposure)
---------------------------------------------------------------------------------------------

I found that coefficients for Year are exactly the same.

I'm wondering if there is any explanation for this? why the coefficients are exactly the same?

Regards,

[Jeph Herrin]

I tried your first model on your data and did not get the same results

. poisson m_all_l1_ause_rr15_c_adj year, exp(m_all_p)
note: you are responsible for interpretation of noncount dep. variable


Poisson regression                              Number of obs     =         27
                                                LR chi2(1)        =       5.14
                                                Prob > chi2       =     0.0234
Log likelihood = -1901.0491                     Pseudo R2         =     0.0013

------------------------------------------------------------------------------------------
m_all_l1_ause_rr15_c_adj |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------------------+----------------------------------------------------------------
                    year |   .0022039   .0009729     2.27   0.023     .0002971    .0041107
                   _cons |  -13.64075   1.946652    -7.01   0.000    -17.45611   -9.825379
             ln(m_all_p) |          1  (exposure)
------------------------------------------------------------------------------------------

[Masoumeh Sanagou]

Thanks for the reply.

I tried one more time and got the previous results.

. poisson m_all_l1_ause_rr15_c_adj year, exposure(m_all_p)
note: you are responsible for interpretation of noncount dep. variable

Iteration 0:   log likelihood = -127.10331 
Iteration 1:   log likelihood = -127.10331 

Poisson regression                              Number of obs     =         27
                                                LR chi2(1)        =     431.15
                                                Prob > chi2       =     0.0000
Log likelihood = -127.10331                     Pseudo R2         =     0.6291

------------------------------------------------------------------------------------------
m_all_l1_ause_rr15_c_adj |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------------------+----------------------------------------------------------------
                    year |   .0191066   .0009262    20.63   0.000     .0172912     .020922
                   _cons |  -47.34115   1.854261   -25.53   0.000    -50.97544   -43.70687
             ln(m_all_p) |          1  (exposure)
------------------------------------------------------------------------------------------

[Joseph Coveney]

why the coefficients are exactly the same?

.ÿ
.ÿclearÿ*

.ÿ
.ÿquietlyÿinputÿintÿYearÿlongÿM_all_Pÿdouble(M_G_High_L1_AUse_RR15_C_adjÿM_all_L1_AUse_RR15_C_adj)

.ÿ
.ÿgenerateÿdoubleÿratioÿ=ÿM_all_L1_AUse_RR15_C_adjÿ/ÿM_G_High_L1_AUse_RR15_C_adj

.ÿsummarizeÿratio

ÿÿÿÿVariableÿ|ÿÿÿÿÿÿÿÿObsÿÿÿÿÿÿÿÿMeanÿÿÿÿStd.ÿDev.ÿÿÿÿÿÿÿMinÿÿÿÿÿÿÿÿMax
-------------+---------------------------------------------------------
ÿÿÿÿÿÿÿratioÿ|ÿÿÿÿÿÿÿÿÿ27ÿÿÿÿ2.366045ÿÿÿÿ4.17e-07ÿÿÿ2.366044ÿÿÿ2.366046

.ÿ
.ÿexit

endÿofÿdo-file


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