PROC UNIVARIATE: Identifying Extreme Observations and Extreme Values

The UNIVARIATE Procedure

Example 4.3 Identifying Extreme Observations and Extreme Values

This example, which uses the data set BPressure introduced in Example 4.1, illustrates how to produce a table of the extreme observations and a table of the extreme values in a data set. The following statements generate the "Extreme Observations" tables for Systolic and Diastolic, which enable you to identify the extreme observations for each variable:

title 'Extreme Blood Pressure Observations';
ods select ExtremeObs;
proc univariate data=BPressure;
   var Systolic Diastolic;
   id PatientID;
run;

The ODS SELECT statement restricts the output to the "ExtremeObs" table; see the section ODS Table Names. The ID statement requests that the extreme observations are to be identified using the value of PatientID as well as the observation number. By default, the five lowest and five highest observations are displayed. You can use the NEXTROBS= option to request a different number of extreme observations.

Output 4.3.1 shows that the patient identified as 'CP' (Observation 7) has the highest values for both Systolic and Diastolic. To visualize extreme observations, you can create histograms; see Example 4.14.

Output 4.3.1 Blood Pressure Extreme Observations

Extreme Blood Pressure Observations

The UNIVARIATE Procedure

Variable: Systolic

Extreme Observations
Lowest			Highest
Value	PatientID	Obs	Value	PatientID	Obs
96	SS	2	130	JW	14
100	FR	3	133	RW	11
108	KD	12	134	JW	16
110	DS	13	140	BL	5
110	JI	8	165	CP	7

Extreme Blood Pressure Observations

The UNIVARIATE Procedure

Variable: Diastolic

Extreme Observations
Lowest			Highest
Value	PatientID	Obs	Value	PatientID	Obs
40	JI	8	80	JW	14
50	DS	13	80	JW	16
50	CK	1	82	HH	22
54	KD	12	90	BL	5
60	RW	11	110	CP	7

The following statements generate the "Extreme Values" tables for Systolic and Diastolic, which tabulate the tails of the distributions:

title 'Extreme Blood Pressure Values';
ods select ExtremeValues;
proc univariate data=BPressure nextrval=5;
   var Systolic Diastolic;
run;

The ODS SELECT statement restricts the output to the "ExtremeValues" table; see the section ODS Table Names. The NEXTRVAL= option specifies the number of extreme values at each end of the distribution to be shown in the tables in Output 4.3.2.

Output 4.3.2 shows that the values 78 and 80 occurred twice for Diastolic and the maximum of Diastolic is 110. Note that Output 4.3.1 displays the value of 80 twice for Diastolic because there are two observations with that value. In Output 4.3.2, the value 80 is only displayed once.

Output 4.3.2 Blood Pressure Extreme Values

Extreme Blood Pressure Values

The UNIVARIATE Procedure

Variable: Systolic

Extreme Values
Lowest			Highest
Order	Value	Freq	Order	Value	Freq
1	96	1	11	130	1
2	100	1	12	133	1
3	108	1	13	134	1
4	110	2	14	140	1
5	112	1	15	165	1

Extreme Blood Pressure Values

The UNIVARIATE Procedure

Variable: Diastolic

Extreme Values
Lowest			Highest
Order	Value	Freq	Order	Value	Freq
1	40	1	11	78	2
2	50	2	12	80	2
3	54	1	13	82	1
4	60	2	14	90	1
5	62	1	15	110	1

A sample program for this example, uniex01.sas, is available in the SAS Sample Library for Base SAS software.

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