The headlines are once again, all ablaze at the projections of a 3.6% retail sales rise from November 1st to December 24th, 2009.

Not so fast. These preliminary numbers are generated from SpendingPulse and the report is not publicly online, so we cannot check the raw report ourselves.

Relying on the media, it appears there was an extra day in the tally and without that extra day, comparing apples to apples vs. oranges from 2008, the actual increase was 1%.

Even more interesting, the above report shows from November 1st to December 24th. The extra day was around Black Friday.

CBSMarketWatch, reporting on Black Friday or November 27th, to December 24th, 2009, without the extra day, holiday sales were actually down.

Without the extra day, the season's growth could have been down by 2% to 4%.

Note, sales are still significantly down from 2007 levels.

How could one day make that large of a percentage difference? Well, each day represents 3.57% of the total number of days. Rounding, that's 3.6%. So, let's assume all sales are evenly distributed across all of the days. This actually isn't true, it's biased higher because of uneven sales volume per day....
but for illustration purposes, assume every day has the exact same amount of gross sales.

Voilà, an instant increase of 3.6% in sales by comparing a time period of 28 days to last year's 27. This is the from Black Friday to December 24th.

Taking the time period to Novemember 1st to December 24th, each day represents 1.85% of sales, assuming even distribution of sales per day. Voilà, without the extra day, in this case, assuming every day sales were the same amount, get a 1.7% total holiday sales increase.

Since the extra day is around Black Friday, one of the biggest sales volume in the year, well, you get the picture on how not comparing the same time period from year to year can really skew results and make for some nice blazing headlines upon which to day trade some retail sales stocks.

Bottom line here is wait for the actual retail sales official reports from the U.S. Department of Commerce.

Hopefully no other supposedly credible surveyor will play such statistical manipulations to get some headline buzz.