Best Christmas gift formula from British psychologist

British psychologist Cliff Arnall derived a formula that should help parents find their child the best toy for Christmas, writes The Daily Telegraph.
Dr. Arnall, who earlier became famous for its formulas best day of the year and the worst day of the year, using well-known principle of value for money, offering to assess quality based on subjective evaluations of toys on the six key characteristics. Arnall included in the formula the following variables:

Pi – useful when playing alone.
Po – useful when playing with other children.
Cr – fostering creativity.
S – promote social interaction with peers.
U – the total value of toys.
H – to convey her brothers and sisters.

Parents need to evaluate each property on a five-point scale and adding these estimates. To results scientist proposes to add the product of two numbers – the average number of hours per month, your child will regularly play with a gift (T) and for how many months it will retain an interest in it (L).
L x T + Pi + Po + Cr + S + U + H
The final amount requested divided by the square root of the price of toys. The choice should be made in favor of the toys, which will result in the highest final grade.  Arnall indicates that the results may be different for different children.