Some populations are “hard to locate,” with nomadic lifestyles that might not involve a regular address. Think of college students in off-campus housing, for example. Others are “hard to contact,” from living in gated areas to facing homelessness. Some people are “hard to persuade,” with a lack of interest in the process. Others are “hard to interview” because of hurdles such as a language barrier or a lack of internet.

COVID-19 adds a new layer of fear to dispel — the worry that an in-person census taker goes door to door and is sick, or violates the new guideline of “social distancing.”

But the census calendar, established long before the coronavirus, outlined how 2020 participants would have choices — online, by mail, by phone or in person. Initial mailings were planned for March 12-20, with online instructions. Three more reminders, as well as the arrival of a paper option that can be returned by mail, are scheduled between mid-March and mid-April.