Seasonality lowers the 2008 projection

An unknown Ken brings up a good point about my annualization of 2008 numbers in an earlier post about exercise. He asks if there is a seasonal effect, for instance, a spike in activity in early January while New Years' resolutions are still fresh. I don't think the particular example is right since I tend to make resolutions like "Spend more time at charity events," or "Save money elsewhere to spend it on occasional fancy groceries," but I acknowledge there may be seasonality.

Other than a consistent spike in July (a beautiful outdoor month in Boston), it's pretty hard to see the pattern in this data.

One thing that is clearly highlighted is my 2007 effort to train for my first marathon (the red line that jumps up in February). I went out hard, and while you'd hope to see that line trending upward as the mid-April race date approached, it actually trended down, revealing the results of my increasing knee pain.

Another big jump comes from a decision to start lifting weights in the spring of 2008. That heightened level of activity may be unsustainable, and points to a regression to pre-2007 levels unless I maintain the weight-lifting goal, or establish a new one.

However, the question remains – is there a difference between the seven months of data I've collected and the rest of the year? This next graph should clarify the issue:

Using this new information, we can prepare new estimates for the 2008 full year. With 205 days on record, we can figure the number of remaining projected workouts by multiplying 60 sessions by (365-205)/205 and then applying a 25% discount and arrive at a total of 35 additional sessions (as opposed to the original estimate of 41).

While this doesn't change the previous conclusions, which were based on year-over-year changes, and not just the 2004-2008 change, it does make the increase in '08 seem more reasonable, although 2008 still projects to be quite an increase over past years: