The Federal Reserve will conclude its final policy meeting of the year Wednesday. With traders widely expecting the central bank to raise short-term interest rates, many say the focus will be on Fed officials’ comments on the economy. Volatile markets and mixed inflation data have amplified investors’ doubts about how many times the Fed can raise rates next year. Also fueling the hesitation are remarks by Chairman Jerome Powell, who said in November that rates looked like they were “just below” neutral, a level that would neither speed nor hamper economic growth.

The...