a decrease in those living below the poverty line

If the poverty line were defined as "household income at the 20th percentile" this wish would be mathematically impossible. In the U.S. the poverty threshold is updated every year and measures well being relative to the increasingly prosperous population across the country.

Such relative measures supply the endless demand for bad news, even if it is such obvious nonsense as "San Francisco is worse than Rwanda".

If instead you would like a dose of good news, research any absolute measure of welfare that you can imagine: television ownership, herd immunity, distance to nearest coffee vendor, number of shoes owned, square feet of living space, quantity of soap used. I have not researched any of these but am certain that the long-term trend is excellent and short-term trends are probably good. It is so obvious and habitual that life is getting better in the long view (until the next catastrophe!) that it is easy to take for granted.

You might also consider people who live outside the country. I see a lot of hand-wringing about the percentage of people who work in this country (as if "work" itself is always good -- usually maybe, but not always). I was just at the World Bank bookstore and picked up an annual report from the IFC. Those quasi-governmental multinationals creep me out, but they do put out pretty booklets. This one says "Since 1990, the number of people living in extreme poverty has been reduced by more than half, and the size of the working middle class in developing countries has nearly tripled."