JitterCalc is a very useful Excel spreadsheet written by
John Mittler, UW Dept. of Microbiology. It allows a user
to jitter data along the
X-axis so that data points no longer completely overlap.
Without jitterin Excel overlaps data points so that they
overlap (see the figure "Original" below). JitterCalc
adds an offset (epsilon) to the X-axis values so they no
longer overlap (see the figure "Jittered" below).
- Sort by x and then by y (from least to greatest) in your spreadsheet.
- Copy (x,y) data from your spreadsheet into columns A and B.
- Adjust "jitter" to change distance between jittered numbers.
- Increase "epsilon" to jitter numbers that are slightly different from each other. Be careful, however, not to make epilson too big. If you make it too big, the graph may get distorted. If in doubt, keep epsilon small.
- Copy results from Column C (yellow) into your spreadsheet.
- Do not copy "FALSE" in last row!
- Program allows you to change white cells only. To modify other parts you will need to turn off "protection" by clicking on Tools/Protection/Protect Sheet.
This sheet can handle a maximum of 2000 points.
Also, if you have >23 points with the same x
value, JitterCalc will center them around the
point instead of the true
midpoint, creating a small positive bias when
there is an even number of points (>=24).
For example, if you have 24 spots on the same
point, JitterCalc will center them around the
12th spot instead of the true mid-point
between 12 and 13. As long as "jitter" is
low, this approximation should be virtually
If either of these maximums
is causing difficulty, call John at (206) 732-6160
and he will tell you how to extend these limits.
This spreadsheet may be distributed free of
charge. Written by John Mittler, June 16, 2001;
modified Dec. 6, 2006