The essence of a scatter plot type diagram is that it visually depicts a relationship between two variables. Even when a pronounced relationship is apparent, there will still likely be many points that don’t fall “on the line”. Often these outliers are of special interest. The code used on these web pages permits interactively identifying the points displayed, including such outliers. This can be done with the aid of the mouse, drawing a rectangle around one or more points, or by name lookup, using a name select list. In addition, certain calculations can be immediately performed on subsets of points, with the results—totals, simple averages, or weighted averages—for multiple subgroups displayed and compared with each other.
All three versions described herein reside in different subdirectories of the website www.polinetworks.com. Each is accessed by appending one of three additions to the basic address, as shown in the first paragraph above. Two of the versions use the same set of data, but present different diagrams based on that data. Specifically, the version at …/math2014 displays a scatter plot of passing rates on the 2014 Texas state math exam, averaged across all grades for each public school district or charter school system. The pass rates are on the vertical axis, with the percentage of students who are classified as economically disadvantaged plotted on the horizontal or x-axis. The version at …/read2014 shows a diagram with the corresponding reading scores for 2014 on the vertical axis. Both the reading and math passing rates are shown in the data grid, along with the percentage of ED students and the district or charter enrollments.
The third version is at …/aa . The variable plotted on the vertical axis of the diagram displayed here is the adjusted allotment for each ISD and charter system for the school year 2015. The adjusted allotment (AA) plays a very important role in Texas’ school finance formula. This diagram will take on meaning after reading some critical analyses of how the AAs for specific school districts are derived, and in particular how the AA that is applied to all charter systems is derived.
The name “ScatterBrain” has been used with several versions of this software. The Java version is described at www.polinetworks.com/SB (case sensitive).
Instructions for using ScatterBrain (js)
(a) Place cursor near a point or points of interest;
(b) Click the left mouse button;
(c) Move the mouse/cursor until the red rectangle encloses the point or points of interest;
(d) Click the left mouse button. One of the points should begin blinking on and off.
(e) If there was more than one point enclosed in the rectangle clicking the LMB once again will advance to the next point found in the rectangle and it will then begin blinking;
(f) Continue until the last point is blinking. Clicking the LMB once more will cause the last point to stop blinking and the process may be repeated.
(a) Place the cursor in the select box window (the first name in the list appears there) and click the LMB;
(b) Scroll to the desired item and click (LMB) on the name; (Note: pressing the letter key corresponding to the first letter of the name being sought will move the list to the names beginning with that letter. This is a lot faster than scrolling down a list of over a thousand names.)
(c) The corresponding point in the graph should begin blinking;
(d) Additional names can be selected and identified by repeating (b);
(e) After no more names are to be selected in this manner click on the [Reset] button before using the mouse identification method again.
(f) To highlight again a point whose name already appears in the select box, it is necessary to double-click the LMB on that name.
(a) Whenever a point is blinking use the mouse to position the cursor at the location where it is desired for the name to begin;
(b) With the cursor in position, press the Ctrl key.
7. Multi-point functions: Clicking on the [Multi] button turns it red, indicating the program is in the mode that operates on a number of points at once, even on all of them. With the Multi function on (red) draw a box around numerous points. (Remember click once, move the mouse, click again.) When the MB is clicked the second time, completing the box, certain calculations will be performed on the row values in each column. Depending on instructions in a “setup file” that the program reads along with the data, the calculation on each column is one of the following three: (a) total; (b) simple (arithmetic) average; (c) a weighted average. With school-related data the most common weighted average is one which weights by the number of students in the school, school district, or charter system. Clicking on the [Notes] button will display information indicating which function is applied to each column in the data grid.
8. Mobil function: When the [Mobil] button is on (yellow) a feature is enabled that helps when using a tablet computer. Several of the data sets being used contain data for charter schools and regular or independent school districts (ISDs). With both [Multi] and [Mobil] on (red and yellow respectively) clicking on [Dist] will show the multi-point calculations for all of the ISDs. They will also be colored aqua. Clicking on the [Chart] button will do the same for the charter schools. These same calculations will be done on a tablet computer if these functions—Multi and Mobil—or both on.
9. The [Ctrl] button: If using a tablet computer touching the [Ctrl] button while one of the dots is blinking on and off will result in the name being written next to the dot. Without a mouse and a keyboard with a Ctrl key, names cannot be positioned precisely on a tablet (as was described in (3) above when using a computer).
10. Senate districts: Clicking the mouse when the cursor is positioned inside the small select box—where “Sen All” appears—causes a list of the 31 Texas senate districts’ numbers to drop down. Clicking on one of them will cause only those school districts or charters which TEA has designated as lying in whole or in part in that senatorial district to be displayed. All of the previously described functions can be used on those points that remain. In particular, the ability to carry out separate tallies on charter schools and ISDs as described in (8) above can prove interesting.
11. Reset button: It was mentioned above that the [Reset] button should be clicked on after using the drop down district name select lists. One other use of the [Reset] button is as follows: if a large number of points have been included in a rectangle and it is not desired to keep clicking the mouse and identifying all of them, clicking on the [Reset] button will jump out of the loop.
13. Final suggestion: Quite often, with comparisons between ISDs and charter schools as the focus, it is helpful to highlight each sector before proceeding (see item 8 above). To do this: (a) turn on both [Mobil] and [Multi] ; (b) click on [Dist]; (c) click on [Chart]. As there are many more regular school districts (ISDs) than charter systems, highlighting the districts first, then displaying the charters on top of them, prevents the districts from obliterating or covering up many of the charter school points. Note: Steps (a) – (c) may already have been performed when the page is first loaded.