# Re: st: incidence rate and confidence intervals

 From moleps <[email protected]> To [email protected] Subject Re: st: incidence rate and confidence intervals Date Mon, 18 Jan 2010 21:41:52 +0100

```I appreciate the inputs, but wouldnt modeling year either by xtpoisson or by dummy-coding, make it "hang tgether" ??

Or would I have to go for a autoregressive Poisson model?

Regards,

//M

On 18. jan. 2010, at 16.00, Nick Cox wrote:

> This doesn't seem to hang together.
>
> The confidence intervals from -ci- treat years separately, i.e. independently.
>
> That's a quite different model from a Poisson regression with -year- as a predictor -- not to mention a custom-built stochastic model that matches epidemiological knowledge for the condition you're studying.
>
> Nick
> [email protected]
>
> Martin Weiss
>
> You can replace your entire loop by
>
> statsby mean=r(mean) ub=r(ub) lb=r(lb), /*
> */  by(year) clear : ci cases,e(pop2) pois
>
> moleps
>
> After scrutinizing the manuals- this is as close as I get:
> gen pop2=population/100000
> capt drop mean up lb
> gen mean=.
> gen up=.
> gen lb=.
>
> forval k=1953/2008{
>
> ci cases if year==`k',e(pop2) pois
> replace mean=`r(mean)' if year==`k'
> replace up=`r(ub)' if year==`k'
> replace lb=`r(lb)' if year==`k'
> }
> sort year
> tw (line mean year) (lowess mean year, lw(thick) bw(0.3)) (lowess up
> year,bw(0.3)) (lowess lb year,bw(0.3)),xlab(1950(10)2010) xlab(,ang(45))
> xtit("Year") ytit("Incidence (per 100,000)") legend(lab(1 Iincidence")
> lab(2 "Lowess") lab(3 "95% CI Upper bound") lab(4 "95% CI Lower bound"))
> leg(col(1))
>
> However looking at the graph and CI´s the upper-limit in the ´50s seem to be
> lower than the lower-limit in the 2000´s, hence contradicting the poisson
> regression model (both by continuous year and as "dummy-years,ie i.year"
> where year is insignificant after correcting for population. I thought
> overlapping CI-lines signified a significant effect or is there a problem
> with the ci-calculations??
>
> On 17. jan. 2010, at 20.11, moleps wrote:
>
>> I´ve got the incidence of a disease in a population in the following data
> format -year,population,cases-
>> I´ve created the incidence rate by dividing cases by population and
> multiplying by 100000.
>>
>> gen ins=(cases/population)*100000
>> poisson cases year population
>>
>> **no tendency for increasing incidense after correcting for population.
>> **however
>>
>> line ins ye
>>
>> **shows an increasing trend. But I´d like to add 95% CI lines to
> corroborate this. Is this at all possible given my dataset??
>
>
>>    |  year   population   cases|
>>        |----------------------------|
>> 1. | 1953    2285542         49 |
>> 2. | 1954    3075055         44 |
>> 3. | 1955    3015476         50 |
>> 4. | 1956    3073404         52 |
>> 5. | 1957    3407827         94 |
>>    |----------------------------|
>> 6. | 1958    3404373         78 |
>> 7. | 1959    3343568         79 |
>> 8. | 1960    3196884         59 |
>> 9. | 1961    3372724         80 |
>> 10. | 1962    3508295         67 |
>>    |----------------------------|
>> 11. | 1963    3348748         84 |
>> 12. | 1964    3680068         72 |
>> 13. | 1965    3594444         85 |
>> 14. | 1966    3270933         67 |
>> 15. | 1967    3668785         66 |
>>    |----------------------------|
>> 16. | 1968    3802479        140 |
>> 17. | 1969    3758948        115 |
>> 18. | 1970    3765404         75 |
>> 19. | 1971    3811994        103 |
>> 20. | 1972    3595579         86 |
>>    |----------------------------|
>> 21. | 1973    3846154         98 |
>> 22. | 1974    3972990        122 |
>> 23. | 1975    3736829        111 |
>> 24. | 1976    4017101        109 |
>> 25. | 1977    4035202         96 |
>>    |----------------------------|
>> 26. | 1978    3972186        100 |
>> 27. | 1979    4066134        110 |
>> 28. | 1980    3813510        111 |
>> 29. | 1981    3908085        121 |
>> 30. | 1982    4029101        126 |
>>    |----------------------------|
>> 31. | 1983    4045128        112 |
>> 32. | 1984    4134353        126 |
>> 33. | 1985    3998700        136 |
>> 34. | 1986    3936817         99 |
>> 35. | 1987    4100854        126 |
>>    |----------------------------|
>> 36. | 1988    4198289        111 |
>> 37. | 1989    4124119        114 |
>> 38. | 1990    4233116        114 |
>> 39. | 1991    4175240         97 |
>> 40. | 1992    4198459        112 |
>>    |----------------------------|
>> 41. | 1993    4124798        113 |
>> 42. | 1994    3986070         95 |
>> 43. | 1995    4348410        109 |
>> 44. | 1996    4369957        135 |
>> 45. | 1997    4392714        135 |
>>    |----------------------------|
>> 46. | 1998    4342720        142 |
>> 47. | 1999    4445329        157 |
>> 48. | 2000    4478497        135 |
>> 49. | 2001    4503436        128 |
>> 50. | 2002    4450334        144 |
>>    |----------------------------|
>> 51. | 2003    4552252        144 |
>> 52. | 2004    4577457        150 |
>> 53. | 2005    4606363        164 |
>> 54. | 2006    4567282        152 |
>> 55. | 2007    4681134        153 |
>>    |----------------------------|
>> 56. | 2008    4571227        150 |
>>    +----------------------------+
>>
>
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```