Reading a series without fooling yourself

• Reading a Rank Chart

  Inverted axis, logarithmic scale, and a small vocabulary of shapes. Getting the presentation right prevents most misreadings before anyone interprets anything.

  Procedure

• Seasonality in Rank Data

  Catalogue-wide demand swings move everyone's rank at once. Failing to account for it produces confident conclusions about individual products every January.

  Analysis

• Comparing Two Products Fairly

  A head-to-head comparison is the most common rank analysis and the easiest to get wrong. Six conditions that have to hold before the comparison means anything.

  Procedure

• When a Change Is Real

  Rank moves constantly with nothing happening. Telling an event from ordinary variation needs a baseline almost nobody establishes.

  Analysis

• How Long to Observe

  The window has to be long enough to average out noise and short enough that the market has not changed underneath it. Both bounds are real and they conflict.

  Procedure

• Estimating Units From Rank, With Error Bars

  It can be done defensibly. What that requires, what the realistic error is, and how to present a number that will not embarrass you six months later.

  Procedure

• A Field Guide to Rank Chart Shapes

  Eight patterns that recur, what each usually means, and the confounder to rule out before believing any of them.

  Reference

7 notes