I made and posted this graph back in 2009. It includes all the elections from 1900 to 2008. The vertical axis is the number of electoral votes for the winner and the horizontal axis is the winners margin of victory expressed as a decimal (0.15 is 15%).
This is the same data seen from the point of view of one party, in this case the Republicans.
The data on this second graph falls roughly on a straight line between -0.10 and +0.10 and from about 100 to 450 EV. Data outside that range tails off and includes the elections that are generally recognized as landslides by most political scientists.
Thanks
