I think most of you have far too broad definitions of a landslide. Really, the word "landslide" indicates a particularly unusual and massive event. Calling 1988 or 1996 "landslides" deprives the word of any meaning.
Over 80% EV.
Over 55% PV.
Margin over 15%.
Those are criterias that make a landslide truly exceptional. That way, only 1928, 1932, 1936, 1956, 1964, 1972, 1984 meet them. 7 elections out of 47 elections (previous to 1824 were not counted due to lack of PV), ie 15%. Under your criteria, more than one third would qualify as landslides.
Any criteria which doesn't call 1920 a landslide must have something wrong with it. 1924 is a strong case too.
I'm not too fond of putting much weighting on EVs, because at that level they're just measuring the distribution of the vote, and I don't think uniform support makes a popular vote landslide much more impressive. It doesn't really give a sense of how easy it would for the trailing candidate to win, unlike other criteria. Other people seem to like it though, probably due to the pretty maps that result.
In any case, rather than have binary thresholds, I think weighting them together is better. 80+55+15 = 150, so an improvement on your criteria could be "If EV% plus PV% plus margin% exceeds 150, then the election is a landslide." That way, 1864, 1920, 1924 and 1980 are all additionally classified as landslides, which seems fair if it's a measure of what "seem like" landslides to most people. You could get fancier but I think this suffices.
Evaluating elections sometmes called landslides based on this method:
2008: 127.94
1996: 128.14
1988: 140.29
1984: 174.58
1980: 151.39
1972: 180.52
1964: 172.93
1956: 158.87
1952: 149.23
1944: 142.29
1940: 149.3
1936: 183.56
1932: 164.07
1928: 159.22
1924: 151.16
1920: 162.59
1912: 138.18
1904: 145.85
1872: 148.68
1864: 156.11
1832: 148.55
According to this method, 1936 was the biggest landslide, with 1972 in second. Borderline (within 2 points) landslides are 1980 and 1924, while borderline not-landslides are 1832, 1872, 1940 and 1952. 2008 and 1996 aren't even close, 2008 in fact gets the lowest score on this list.
