For its Black Friday predictions, dealnews uses up to two years of historical data based on deals listed on dealnews.com.
To make a prediction, dealnews takes these measures:
- How much have prices fallen this year to date?
- How much did prices fall at this time last year?
- How much more did they fall on Black Friday last year?
- How much did they fall the preceding year?
Using that data, we extrapolate prices for this Black Friday by applying current trends to historical Black Friday price drops. In so doing, we correct for anomalies like outliers, floor effects, and disruptive new technologies that influence pricing trends. We also usually round to the nearest dollar amount ending in a "9" since retailers overwhelmingly do the same.
ACCURACYdealnews defines accuracy for its Black Friday Predictions of 2009 in the following manner:
- The predicted price was within ±10% of the observed price
- Predictions with no data are excluded (e.g., retailers had no notable desktop PC sales during Black Friday 2008, so the accuracy of dealnews' 2008 desktop PC prediction was not evaluated)