Federal Reserve Board Chairman Jerome Powell reacts after the two-day meeting of the Federal Open Market Committee on interest-rate policy on June 13, 2018, when it raised its benchmark rate to 1.75% to 2%. If the Fed cuts this week, the rate will return to that level.

If the trend persists, it could be worrisome for the market. Powell's public schedule will accelerate in 2019, when he starts hosting news conferences after every meeting rather than just quarterly.

When he delivers congressional testimony or other speeches, the average decline is 0.4 percentage point, with the index falling 5 out of the 9 occasions. Adding up the occasions when Powell has spoken publicly equaled the $1.5 trillion figure.

The bank's strategists specifically found that when Powell gives a news conference after a Federal Open Market Committee meeting , the typically drops 0.44 percentage point and has fallen each of the three times he has spoken to the media.

Since the central bank chief took over in February, his public remarks have cost the market dearly — specifically about a $1.5 trillion loss in market cap, according to a J.P. Morgan analysis.

The possible reason for the decline, according to the analysis: Worry that Powell and the Fed by extension aren't understanding the current landscape.

"Specifically, the equity market likely implies that the Fed is underestimating various risks, and hence is increasing the implied probability of the Fed committing a policy error in the future," Marko Kolanovic, global head of quantitative and derivatives strategy, wrote in the report. "A higher probability of a policy error translates into lower equity prices on the news."

Overall, the market has done quite well this year.

The S&P 500 has risen about 9.6 percent, even though the Fed has increased interest rates three times. Powell has repeatedly said that he believes the economic outlook is strong and that this is a good time for the central bank to normalize policy after years of an ultra-accommodative stance.

However, the market hasn't liked what it has heard specifically from him — and neither has President Donald Trump.

Trump has criticized the Fed on several occasions, a move unusual for a president, saying he is worried the Fed's insistence on raising interest rates could cost the economy the substantial momentum it has built up since the 2016 elections.

The J.P. Morgan paper said there appears to be direct causation between Powell's remarks and stocks because the market had taken a discernible change in direction during the days when the Fed chief spoke.

The bank cited three troublesome statements from Powell: That stocks are overvalued, that multiple rate hikes are needed or necessary, and that a stock market "sell-off warrants attention if sustained." Kolanovic said that implies the Fed doesn't understand market structure and may stay on the sidelines too long.

"If fundamental investors start questioning the cycle, a technically driven sell-off could be more violent and more likely to deliver a knock-out punch to the economic cycle," he wrote. "The new microstructure of financial markets would not leave enough time for the Fed to react."

CNBC has contacted the Fed for comment.

WATCH: Powell says too early to see trade policy effects on economy