Hi Marty,
I find Bubble Charts one of the most powerful and difficult reports to work with. I think the main trick is to create dispersion, in order to separate what's being compared into different quadrants. To do that, each item needs some mechanism to give it both a variable value on the Y and X axis.
As an example, here is a video showing a Bubble Chart that I developed for monitoring Issues. The Bubble sizes are driven by the number of Planned Hours it will take to solve the Issue. The Bubble colors are the Priority of each Issue, which is excellent for "toggling". The X axis is the number of days early until (positive) or late (negative) each issue is, relative to its due date (zero). The Y axis is a calculation of the importance of the Issue, which is primarily driven off the priority of the issue, but also takes the Issue's due date into mind: the further away it is, the lower that importance (in fact, decreasing to zero 90 days out, meaning "too far out to worry about yet"), and then gradually "floating" higher as the due date approaches, peaking at a known amount "on" the due date (which varies by priority; e.g. Urgent = 100000, High = 80000, Normal = 50000, Low = 30000). Once it's late, the slope of the float INCREASES for Urgent/High/Normal items, but DECREASES for Low items, the latter sinking into the backlog. In this manner, the priority of what to work on becomes obvious: using the axis to divide the work into quadrants, the top left is high priority and late, top right is important, with the left side being due soonest, and the bottom left is least important (the backlog). Once items start "bumping" against the far right (arbitrary) wall -- 90 days late, in my example -- it's time to get real: these one's are NOT getting done, so either reset the due date into the future, or kill them. And finally, as per the video, the prompts on the chart for priority, height, and time frame effectively allow users to "zoom in" on whatever is of interest to them (e.g. "show only Urgent in the top left quadrant"). In fact, I set up a dashboard that opens (by default) to show everything in a chart at the top, and then six "zoomed in" charts, like this, allowing quick triage of what's going on:
---BIG CHART --
--------top left-------- ------top middle----- -------top right-------
------bottom left----- ---bottom middle--- ----bottom right----
Incidentally, I got this idea for this from the coolest Bubble Chart I've ever seen and someday, intend to animate my Workfront bubble charts in a similar manner.
So! With that primer in hand, back to your original question about Project Prioritization. As part of JITR , we use a concept called Project Priority Indicator, which effectively forces the vertical distribution (bubble chart-wise) of every Project. It can be a simple manually entered numeric ordinal, or a complex formula that uses custom data drivers, portfolio weights, and/or portfolio optimizer rankings: the point is, every Project's importance will vary: that's the Y axis (noting that Project "value" is also an excellent standalone, less contentious candidate). The X axis can then be time based -- e.g. Planned Completion date, similar to my Issue example -- but could also be in number of days (e.g. "days until decision date" is a good one for sales based projects); but using something like a confidence level (thinking of classic sales funnels) also makes a good option. The size of each bubble could be value, or cost, or hours, or some calculated field, and the color (I've come to learn) works best with out of the box fields such as priority (which have standard colors), since although you can use a calculated field in a grouping for the colors, they can quickly exceed the relatively low limit, and the chart will refuse to render with a "Woah..." message.
Thanks for raising such an interesting question: I've been meaning to blog about this for ages, and think this pretty much covers what I had in mind!
Regards,
Doug
