When make a Scatter Dot Plot together with mean values and Standard Deviation it looks fine. However, if I change to Standard Error the error bars actualy become much smaller than the true Standard Error. Is this a bug or am I doing something wrong. I enclose an illustration of the problem. The data in wave A6 has a Mean Value of 1.485, a Standard Deviation of 0.447 and a Standard Error of 0.075. The Mean Values and Standard Deviation are shown correctly in the left graph but the right graph indicates a Standard Error of 0.0128 (measured with Show Info) rather than 0.075.
Standard deviation is simply the standard deviation of your raw data. The Standard Error is more properly called Standard Error of the Mean; it is stdev/(N-1) where N is the number of data points. If your data follow nice Gaussian statistics, it is an estimate of how well you know the "true" mean value of the supposed underlying distribution from which your data were drawn.
Sure enough- the author of the Scatter Dot Plot package made the same mistake I did. I have corrected the error, and attached a fixed procedure file. You will find the procedure file in Igor Pro Folder:WaveMetrics Procedures:Graphing: Simply replace that copy with the one attached.
John Weeks
WaveMetrics, Inc.
support@wavemetrics.com
October 18, 2017 at 10:06 am - Permalink
I think that's a bug. I use scatter dot plot a lot but I always use s.d. for the error bars, but I can reproduce what you see in IP7.05 on macOS.
John, s.e.m. is stdev/sqrt(n). But even so, the standard error calculated by the scatter dot plot package is out.
•wavestats dd
V_npnts= 20; V_numNaNs= 0; V_numINFs= 0; V_avg= 10.2673;
V_Sum= 205.346; V_sdev= 1.08918; V_sem= 0.243549; V_rms= 10.322;
V_adev= 0.82628; V_skew= -0.0352432; V_kurt= -0.77727;
V_minloc= 15; V_maxloc= 12; V_min= 8.30005; V_max= 12.1819;
V_minRowLoc= 15; V_maxRowLoc= 12; V_startRow= 0; V_endRow= 19;
// make a scatter dot plot using the GUI
// print the magnitude of error plotted by the package
•print root:Packages:WMScatterDotPlot:Graph0:counts_ddSy[2]-root:Packages:WMScatterDotPlot:Graph0:counts_ddSy[3]
0.0573254
October 18, 2017 at 12:17 pm - Permalink
Oops. Of course. I'll look at the Scatter Dot Plot package.
John Weeks
WaveMetrics, Inc.
support@wavemetrics.com
October 18, 2017 at 12:36 pm - Permalink
John Weeks
WaveMetrics, Inc.
support@wavemetrics.com
October 18, 2017 at 12:54 pm - Permalink
Erik
October 20, 2017 at 02:15 am - Permalink