Help using Base SAS procedures

Trend test for Incidence rates over the years

Accepted Solution Solved
Reply
Contributor
Posts: 59
Accepted Solution

Trend test for Incidence rates over the years

 

Hi,

I need advice about how to calculate a significance test (trend test) for comparing the incidence rates over the years. I need to comment on whether there is a significant increase or decreas (with p-value for a trend) for incidence rates over the years.

 

Please see the attached data. My denominator for incidence is 100,000 for all.

 

I would really appreciate if anyone can help me with the SAS code.

 

Thanks,

Satish


Accepted Solutions
Solution
‎11-24-2015 03:43 PM
Esteemed Advisor
Posts: 5,535

Re: Trend test for Incidence rates over the years

Posted in reply to smunigala

A popular test for detecting trends in timeseries is the Kendall Tau-b correlation, available in proc corr and proc freq :

 


proc corr data=trendtest kendall;
var year; with amortality_pan;
run;

 

 

PG

View solution in original post


All Replies
Valued Guide
Posts: 864

Re: Trend test for Incidence rates over the years

Posted in reply to smunigala

You should give more information regarding the calculations.  While I'm sure there are several that know exactly what you want I do no. 

Contributor
Posts: 59

Re: Trend test for Incidence rates over the years

Posted in reply to Steelers_In_DC

Thanks for the reply. The incidence rates are the trends for acute pancreatitis deaths nationally over the years. I wanted to know if there is an increase or decrease in trend over the years. The incidence rates are adjusted for 2010 population (national US population).

 

 

Esteemed Advisor
Posts: 5,535

Re: Trend test for Incidence rates over the years

Posted in reply to smunigala

What have you tried, so far?

PG
Contributor
Posts: 59

Re: Trend test for Incidence rates over the years

I have not done the trend test for comparing rates over the years to check for significance. However, I did Cochran- Armitage Trend test previously for categorical variable. So I am not sure how to do this. I looked up some online blogs about linear regression analysis but not entirely sure. I hope this helps.

 

Thanks!

Solution
‎11-24-2015 03:43 PM
Esteemed Advisor
Posts: 5,535

Re: Trend test for Incidence rates over the years

Posted in reply to smunigala

A popular test for detecting trends in timeseries is the Kendall Tau-b correlation, available in proc corr and proc freq :

 


proc corr data=trendtest kendall;
var year; with amortality_pan;
run;

 

 

PG
New Contributor
Posts: 2

Re: Trend test for Incidence rates over the years

Hi, I have a similar question like this. After doing this step, how could I interpret the 0.4463? What is the trend for the data? Since the prevalence or the incidence are not normally distributed, could I just use Simple Regression Model and get the coefficient for the trend? Or is there any other suggestion for this situation? I have a sample data like below. Thanks a lot. 

Kendall Tau b Correlation Coefficients, N = 41
Prob > |tau| under H0: Tau=0

 

Year

Prevalence

0.44634
<.0001

YearPrevalence
197416.943
197519.6
197618.934
197718.48
197819.924
197912.369
198017.302
198115.954
198216.75
198317.184
198417.722
198519.008
198618.452
198716.744
198817.029
198917.643
199017.179
Esteemed Advisor
Posts: 5,535

Re: Trend test for Incidence rates over the years

You will get a lot more attention if you submit your question as a new topic.

 

You can get a robust estimate of the slope called Sen's slope (or the Kendall slope estimator) as:

 

proc sql;
create table slope as
select 
    median( (b.prevalence-a.prevalence) / (b.year-a.year) ) as senSlope
from
    myData as a inner join 
    myData as b on a.year < b.year;
select * from slope;
quit;
PG
Contributor
Posts: 59

Re: Trend test for Incidence rates over the years

HI PGStats,

Can you please respond to my other post "Trend Test for Incidence"

 

Thanks you!

New Contributor
Posts: 2

Re: Trend test for Incidence rates over the years

Thanks a lot. It works and report a number 0.189. Could I interpret 0.189 as each year the prevalence is increasing 0.189 (the annual year of change). Is that correct? I really appreciate for your help.

 

 

Esteemed Advisor
Posts: 5,535

Re: Trend test for Incidence rates over the years

I( guess so. But I haven't seen your code, or your full dataset. Make sure you understand what you are doing.

PG
Esteemed Advisor
Posts: 5,535

Re: Trend test for Incidence rates over the years

Posted in reply to smunigala

Did something happen around 2001?

 

SGPlot1.png

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

If so you should test before and after separately:

 

libname xl Excel "&sasforum.\Datasets\Trendtest.xlsx" access=readonly;

proc sql;
create table trendtest as
select *, year>=2001 as period from xl.'Sheet1$'n;
quit;

proc sgplot data=trendtest;
scatter x=year y=amortality_pan;
refline 2001 / axis=x;
run;

proc corr data=trendtest kendall;
by period;
var year; with amortality_pan;
run;
PG
Contributor
Posts: 59

Re: Trend test for Incidence rates over the years

Hi PGStats,

Thanks for the response. I am not sure if there was anything significant in 2001 but recently over the years, the trends decreased due to improved diagnostic tests.

 

Satish

☑ This topic is solved.

Need further help from the community? Please ask a new question.

Discussion stats
  • 12 replies
  • 4470 views
  • 2 likes
  • 4 in conversation