Our Metrics intern, Eric Hergenrader, did some terrific work analyzing fluctuations in Firefox usage.  Using a linear regression, he found that this summer’s decline in Firefox use was largely in line with expectations; a 2-3% decline in July and August is typical.  In addition to seasonality, Eric found that three factors driving usage drops are weekends (-18%), holidays (-30%), and Firefox releases (-13.5%).

Two months later, Eric’s model does a remarkable job predicting future usage.  Below, I have plotted actual against predicted usage.  The correlation between these two lines is remarkable.  Since September, the average prediction was off by just 1.63%!

To better understand daily growth variations, I created a heat map that visualizes month over month usage growth. Each cell contains one day’s growth rate over the same day of the week, 28 days earlier.

Some highlights:

• Strongest growth occurs during Spring and Fall
• Periods of growth and decline are clustered
• Growth is outperforming predictions by 2.58%

We must be careful not to overreach with our conclusions.  We are working with a limited range of data and have likely missed significant confounding variables.  That said–thanks to Eric’s work–we’re off to a great start.  Please leave your thoughts and any suggestions on how to improve our projections in the comments.