Discussion of noise in year to year updates of CPS

[fgregg]

CPS recalculates the tiers every year using popstats and previous year test scores of students from a census tract.

Both types of data are noisy.

Might be worth adding a discussion of this noise. Effective visualisation might be to show linecharts for each tier that has changed in the past four years or so. Many of these will bounce around.

Thoughts @mccc