The useful numbers for decision making are "how many people could be helped by addressing this issue?"
No, the first and primary useful number consideration is, "Now that we're 20 TRILLION dollars in debt and most new jobs are low-paying junk that barely creates any tax revenue, and we have an exploding entitlement spending problem the mere interest on the debt for which will soon displace nearly all discretionary spending ... what can we afford to research?"
You want to address the X in Y cases of Z disease in given populations? Return to producing the sort of economic health and largess that allows us to spend that kind of money in the first place. Otherwise, it's like a bankrupt person trying to decide whether to buy a new raincoat or an umbrella so they don't get their nice to outfit wet, because, you know, priorities. A house in fiscal order can spend vastly more money on everything from pure medical research to Mars missions without crushing the very economy that underwrites such things.