I'm saying this since I have a couple of friends who are odd makers and work for the largest casino chain here in Mexico (Caliente). They told me that the main factors which are considered when they are going to publish for the very first time a line are stats, projections, casino's benchmarkings and their sport knowlage. Of course, when you look at handicap bet lines, they try to balance the lines in order to make them attractive but still the +\- points/runs/goals etc given to a team are based on what I just explained. On the other hand some handicap bets like over/under, have their standards based mainly on history. For example, the over/under for soccer games is usually 2.5 goals and so on.