DemFromCT at dailykos has an informative commentary on the variable factors being weighed, and how they are differently interpreted by Democrats, Republicans and non-partisan professionals. In the end, someone's right and someone's wrong. If the Republicans retain the House, there are going to be a good number of embarrassed professional and academic prognosticators. OTOH, whereas most of the reasons to believe there's a strong Democratic wave are based on published data, the reasons for Republican optimism are based on conjecture, anectodes, head games and fear.
SPECIAL DEAL: Subscribe to our award-winning print magazine, a publication Bernie Sanders calls "unapologetically on the side of social and economic justice," for just $1 an issue! That means you'll get 10 issues a year for $9.95.