Programming the statistical procedures from SAS

How to compare two rates in SAS - Need Help, Please

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Contributor
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Accepted Solution

How to compare two rates in SAS - Need Help, Please

I know this may be a simple answer, but I cannot seem to find what I am looking for via my internet searches and thought I would ask here.

I have two datasets. Each dataset has an up to date vaccine variable. There is one dataset for year 2010 and one dataset for year 2011.

I am wanting to see if the rate of individuals that were up to date in year 2010 is significantly different compared to the rate of the individuals up to date in year 2011.

Year 2011     UTD Variable

                              0                    30

                              1                    80

37.5% were up to date

Year 2010     UTD Variable

                              0                    50

                              1                    75

66.67% were up to date

I was able to test if the difference between those were up to date and those who were not was statistically significant by using proc freq  and the chisq option.

Just not sure how to compare rates from two different datasets.

Thank you for any help you can provide.


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Solution
‎10-12-2011 09:54 PM
Super User
Super User
Posts: 6,136

Re: How to compare two rates in SAS - Need Help, Please

Not sure what test you want.  Here is how to do a CHISQ test.

data have ;

  input year utd count;

cards;

2011 0 30

2011 1 80

2010 0 50

2010 1 75

run;

proc freq ;

  weight count;

  tables year*utd / chisq;

run;

The FREQ Procedure

Table of year by utd

year      utd

Frequency|

Percent  |

Row Pct  |

Col Pct  |       0|       1|  Total

---------+--------+--------+

    2010 |     50 |     75 |    125

         |  21.28 |  31.91 |  53.19

         |  40.00 |  60.00 |

         |  62.50 |  48.39 |

---------+--------+--------+

    2011 |     30 |     80 |    110

         |  12.77 |  34.04 |  46.81

         |  27.27 |  72.73 |

         |  37.50 |  51.61 |

---------+--------+--------+

Total          80      155      235

            34.04    65.96   100.00

Statistics for Table of year by utd

Statistic                     DF       Value      Prob

------------------------------------------------------

Chi-Square                     1      4.2210    0.0399

Likelihood Ratio Chi-Square    1      4.2567    0.0391

Continuity Adj. Chi-Square     1      3.6732    0.0553

Mantel-Haenszel Chi-Square     1      4.2031    0.0404

Phi Coefficient                       0.1340

Contingency Coefficient               0.1328

Cramer's V                            0.1340

       Fisher's Exact Test

----------------------------------

Cell (1,1) Frequency (F)        50

Left-sided Pr <= F          0.9861

Right-sided Pr >= F         0.0273

Table Probability (P)       0.0134

Two-sided Pr <= P           0.0531

Sample Size = 235

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Grand Advisor
Posts: 16,878

Re: How to compare two rates in SAS - Need Help, Please

As far as I know you can't.

You'll need to get them into a single dataset...there's a ton of ways to do this but one way is to set the data together and include the year, then run proc freq. 

Respected Advisor
Posts: 2,994

Re: How to compare two rates in SAS - Need Help, Please

How about PROC COMPARE? This assumes you have one row in each table for each individual and you have a common key identifying the individuals. You can also configure the method used to identify differences and the size of the difference.

proc compare base = dataset2010

             compare = dataset2011

             out = difs

             OUTNOEQUAL LISTEQUALVAR LISTCOMPVAR LISTBASEVAR

             MAXPRINT=300

             ;

  id individual_ID;

  var rate;

  where UTD = 1;

run;

Contributor
Posts: 71

How to compare two rates in SAS - Need Help, Please

I will have to try this method and see how it works. I have not yet been able to try it on my data but will let you know if it works out. thank you for the suggestion!

Solution
‎10-12-2011 09:54 PM
Super User
Super User
Posts: 6,136

Re: How to compare two rates in SAS - Need Help, Please

Not sure what test you want.  Here is how to do a CHISQ test.

data have ;

  input year utd count;

cards;

2011 0 30

2011 1 80

2010 0 50

2010 1 75

run;

proc freq ;

  weight count;

  tables year*utd / chisq;

run;

The FREQ Procedure

Table of year by utd

year      utd

Frequency|

Percent  |

Row Pct  |

Col Pct  |       0|       1|  Total

---------+--------+--------+

    2010 |     50 |     75 |    125

         |  21.28 |  31.91 |  53.19

         |  40.00 |  60.00 |

         |  62.50 |  48.39 |

---------+--------+--------+

    2011 |     30 |     80 |    110

         |  12.77 |  34.04 |  46.81

         |  27.27 |  72.73 |

         |  37.50 |  51.61 |

---------+--------+--------+

Total          80      155      235

            34.04    65.96   100.00

Statistics for Table of year by utd

Statistic                     DF       Value      Prob

------------------------------------------------------

Chi-Square                     1      4.2210    0.0399

Likelihood Ratio Chi-Square    1      4.2567    0.0391

Continuity Adj. Chi-Square     1      3.6732    0.0553

Mantel-Haenszel Chi-Square     1      4.2031    0.0404

Phi Coefficient                       0.1340

Contingency Coefficient               0.1328

Cramer's V                            0.1340

       Fisher's Exact Test

----------------------------------

Cell (1,1) Frequency (F)        50

Left-sided Pr <= F          0.9861

Right-sided Pr >= F         0.0273

Table Probability (P)       0.0134

Two-sided Pr <= P           0.0531

Sample Size = 235

Grand Advisor
Posts: 9,451

Re: How to compare two rates in SAS - Need Help, Please

There is a problem. That is correlation.

If these two year's experiments were applied at the same patient. then there is a correlated effect.

You can not directly use these data into proc freq .

Need to subtract between them to remove this correlated effect.

Ksharp

Contributor
Posts: 71

How to compare two rates in SAS - Need Help, Please

Thank you pointing this out Ksharp. I need to keep this in mind and take into account the correlated effect.

Esteemed Advisor
Posts: 7,057

Re: How to compare two rates in SAS - Need Help, Please

I've never tried this, but just found it in a 2007 SAS-L thread.  I think you should just get the numbers from running the two proc freqs and then apply them to a "proportions test".

Here is what I discovered in that 2007 thread:

Try the SAS built-in tool for proportion test.  It's under

Solutions-->Analysis-->Analyst to open the Analyst Window; then

Statistics-->Hypothesis Tests--> One-Sample (or Two-Sample) Test for

Proportions.  You can only test the equality of proportions between two

regions each time (I am not sure if this is true or I haven't just

found the right option)

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