In this hack you can see:
$activity01= $userinfo[posts]-$starts;
$activity02= $starts;
$activity03= $personal0[personalviews];
$personal= 3*$activity02+2*$activity01+$activity03;


$activity01 is a stuff that the user's replies to others.

$activity02 is a stuff that the user start threads.
$activity03 is a stuff that the threads started by this user have been viewed by others .

$personal is a value that above.you can difinite the
$personal= 3*$activity02+2*$activity01+$activity03;
as you like.