Perfect presents

eBay claims it has cracked the formula for Christmas shopping success.

Yes that's right, the online auction site consulted Tokyo-based mathematician Philip Obayda and psychologist Dr David Lewis to identify seven key factors in the choosing of original, but suitable gifts.

Apparently, the correct formula is:

((R+D)/S) + ((2(SQ+PT+T))/(0+1))

But of course! This is what the letters mean:

R =      Relationship Rating: How strong your relationship is with the recipient
S =      Scrooge Factor: How mean or generous you are
D =      Difficulty Determinate: Breadth of Interests of recipient
SQ =     Squeal Factor: Projected intensity/pleasure of the opening experience
T =      Time Test: The time and thought expended on selecting the gift
PT =     Personal Touch: Care taken to ensure gift is relevant to the receiver
O =      Originality Axis: How original vs predictable the gift is

To use the formula, you need to rate each of the questions on a scale of 1 to 5; where 1 = not true and 5 = completely true. Once you have rated the factors, simply add your scores into the formula and obtain the gifts rating.

eBay says it found that, for men, clothing knitted by elderly relatives averages a score of 2, while signed sports memorabilia averages a score of 24.