Population loss, he says, has been driven by historic decreases in household size. In 1970, Baltimore averaged 3.07 persons per household. By 2010, the average was 2.38. But by last year, it was 2.23. That last drop in household size, he says, meant a loss of about 10,000 people per year. And that means the city has to add between 5,000 and 6,000 households annually just to hold population.