When you specify the CROSSREF=YES option in the PLOT statement in PROC POWER, a reference line is added from the intersection point on each power curve to X axis indicating the solution for the specified REF= value. However, the displayed value on the reference line might not match the value displayed in the tabular output of PROC POWER. In general, the power or sample size displayed in the PROC POWER table is more precise and is the value to use rather than the approximated value displayed in the graph. Sometimes the difference in these values can be substantial.

The following sample program illustrates this.

      proc power; 
         twosamplefreq test=pchi 
                       proportiondiff = 0.15 0.2 0.3 
                       refproportion = 0.4 
                       ntotal = . 
                       power = 0.9; 
         plot y=power min=0 max=1 yopts=(ref=0.9 crossref=yes) vary(symbol); 
         run;

The values displayed in the plot are linearly interpolated from the two neighboring points on each curve rather than being computed directly from the power formula. However, the values in the preceding table are directly computed from the formula.

Computed N Total Index Proportion Diff Actual Power N Total 1 0.15 0.900 462 2 0.20 0.902 260 3 0.30 0.902 112

Operating System and Release Information

Product Family	Product	System	SAS Release
			Reported	Fixed*
SAS System	SAS/STAT	Microsoft Windows 2000 Advanced Server
		Microsoft Windows 95/98
		Microsoft Windows 8.1 Pro x64
		Microsoft Windows 10
		Microsoft Windows 8.1 Pro 32-bit
		Microsoft Windows 8.1 Enterprise x64
		Microsoft Windows 8.1 Enterprise 32-bit
		Microsoft Windows 8 Pro x64
		Microsoft Windows 8 Pro 32-bit
		Microsoft Windows 8 Enterprise x64
		OS/2
		Microsoft Windows 8 Enterprise 32-bit
		Microsoft® Windows® for x64
		Microsoft Windows XP 64-bit Edition
		Microsoft Windows Server 2003 Enterprise 64-bit Edition
		Microsoft Windows Server 2003 Datacenter 64-bit Edition
		Microsoft® Windows® for 64-Bit Itanium-based Systems
		OpenVMS VAX
		z/OS 64-bit
		z/OS
		Microsoft Windows 2000 Datacenter Server
		Microsoft Windows 2000 Server
		Microsoft Windows 2000 Professional
		Microsoft Windows NT Workstation
		Microsoft Windows Server 2003 Datacenter Edition
		Microsoft Windows Server 2003 Enterprise Edition
		Microsoft Windows Server 2003 Standard Edition
		Microsoft Windows Server 2003 for x64
		Microsoft Windows Server 2008
		Microsoft Windows Server 2008 R2
		Microsoft Windows Server 2008 for x64
		Microsoft Windows Server 2012 Datacenter
		Microsoft Windows Server 2012 R2 Datacenter
		Microsoft Windows Server 2012 R2 Std
		Microsoft Windows Server 2012 Std
		Microsoft Windows Server 2016
		Microsoft Windows Server 2019
		Microsoft Windows XP Professional
		Windows 7 Enterprise 32 bit
		Windows 7 Enterprise x64
		Windows 7 Home Premium 32 bit
		Windows 7 Home Premium x64
		Windows 7 Professional 32 bit
		Windows 7 Professional x64
		Windows 7 Ultimate 32 bit
		Windows 7 Ultimate x64
		Windows Millennium Edition (Me)
		Windows Vista
		Windows Vista for x64
		64-bit Enabled AIX
		64-bit Enabled HP-UX
		64-bit Enabled Solaris
		ABI+ for Intel Architecture
		AIX
		HP-UX
		HP-UX IPF
		IRIX
		Linux
		Linux for x64
		Linux on Itanium
		OpenVMS Alpha
		OpenVMS on HP Integrity
		Solaris
		Solaris for x64
Tru64 UNIX

* For software releases that are not yet generally available, the Fixed Release is the software release in which the problem is planned to be fixed.

---

proc power; 
      twosamplefreq test=pchi 
         proportiondiff = 0.15 0.2 0.3 
         refproportion = 0.4 
         ntotal = . 
         power = 0.9; 
         plot y=power min=0 max=1 yopts=(ref=0.9 crossref=yes ) vary (symbol); 
run; 

Using the CROSSREF option in the PLOT statement in PROC POWER might return values that do not match the results in the PROC POWER table output.

Type:	Usage Note
Priority:
Topic:	SAS Reference ==> Procedures ==> POWER Analytics ==> Power and Sample Size

Date Modified:	2019-04-23 08:39:51
Date Created:	2008-06-30 13:36:18