topic Re: Proc Means confidence limit gives "." in SAS Procedures

Proc Means confidence limit gives "."

ST1 — Wed, 23 Mar 2016 22:52:38 GMT

Hi Everyone,

I am trying to get the 95% confidence interval for a disease severity progression data set in SAS 9.4. The data have been log transformed and are not normal (certain weeks have a lot of 0 values). Sometimes the confidence limit output contains "." rather than numbers. In the year 2 output it seems that this only happens when the disease severy mean in 0 (see year 2 below), but in the year 1 data it happens for weeks when the disease severity mean is 0.3010 or 0 (see year 1 below). My question is: what does the "." mean? Why is a "." returned even when the mean is not 0?

Thank you

Sherri 🙂

This is the coding for year 2:

Title2 "Confidence Interval";
proc means data= first maxdec=4 alpha=0.05 clm mean;
class trt;
var jul23 jul31 aug6 aug13 aug20 aug27 sep3 sep10 sep17;
run;

and this is part of the output:

Coding for year 1

Title2 "Confidence Interval";
proc means data= first maxdec=4 alpha=0.05 clm mean;
class trt;
var aug21 aug30 sep14 sep24 oct11;
run;

Output for year 1:

Re: Proc Means confidence limit gives "."

Astounding — Wed, 23 Mar 2016 20:12:12 GMT

Is it possible you have missing values in your data? If only one observation has a nonmissing value, you can get a mean. But you can't get confidence limits. Perhaps you could check your data for a few of these cases.

Re: Proc Means confidence limit gives "."

ST1 — Wed, 23 Mar 2016 20:26:09 GMT

There are 3 missing values in the year 1 data set (Oct 11 trt 2, and Sept 24 and Oct 11 trt 3), but they don't seem to correspond to the missing values in the confidence limit output. If it helps provide context, both data sets have 7 trt and four reps

Re: Proc Means confidence limit gives "."

Astounding — Wed, 23 Mar 2016 20:42:19 GMT

Perhaps you could share some of the data. There are other conditions where there would be a mean but no confidence limit, such as all values being identical. Are you able to share all the data points for one set of values that has no confidence limits?

Re: Proc Means confidence limit gives "."

Reeza — Wed, 23 Mar 2016 21:45:18 GMT

Add Standard Deviation to the chart please and repost.

Re: Proc Means confidence limit gives "."

ST1 — Wed, 23 Mar 2016 22:51:27 GMT

Here is data for trt 7 of year 1

block trt  aug21 aug30 sep14 sep24 oct11;
1	7	0	0	0.2	0.5	1
2	7	0	0	0	0.6	1
3	7	0	0.1	0	0.9	1
4	7	0	0	0	0.5	1
;

Re: Proc Means confidence limit gives "."

ST1 — Wed, 23 Mar 2016 22:53:24 GMT

Please see orginal message for update chart.

Re: Proc Means confidence limit gives "."

Reeza — Thu, 24 Mar 2016 00:25:10 GMT

Do you see the issue? 🙂

All results with missing CI have a standard deviation of 0 - implying that the values are all that single value.

Re: Proc Means confidence limit gives "."

Ksharp — Thu, 24 Mar 2016 05:50:10 GMT

As Reeza pointed out . You can not calculated CI when it is at the highest level (nway), there is only one obs for that. Specify WAYS statement.

proc means data= first maxdec=4 alpha=0.05 clm mean;
class trt;
ways 1 ;
var jul23 jul31 aug6 aug13 aug20 aug27 sep3 sep10 sep17;
run;