Beginning with the definition of such:
"Missing Middle” is a term that refers to the range of housing types that fit between single-family detached homes and mid-to-high-rise apartment buildings. Used in this context, “middle” references the size and type of a home, and its relative location – in the middle – on a spectrum of housing types. These housing types are commonly house-scaled buildings, yet with more than one unit. Examples include duplexes, triplexes, townhomes, and others that will be discussed in this report. The cost of these housing types varies based on style, size, location, and market forces. Missing Middle (MM) housing types do not always correlate with a specific income bracket but can be less expensive than other housing options that are larger and take up more land.
It is somewhat inaccurate to equate "missing middle" with middle-class housing (as I have done a few times), but the correlation with median income is not too far off the mark. Understand, much of this study involves "taking the pulse" of existing community members, and you will see a lot of common complaints (traffic, overcrowded schools, loss of green space and canopy). I won't say these are not legitimate complaints, but I will say that many citizens use them as a crutch when they are really concerned about "those people" moving in. Here are the main choices Arlington found to increase the missing middle: