Americans' confidence in the economy remains higher than it was before the Democratic convention, according to polling firm Gallup.

Its U.S. Economic Confidence Index averaged -12 for the week ended Aug. 14, similar to the -10 in its late July rally and in the first week of August, but above the -16 average for the six weeks leading up to the convention.

The Democratic Party formally nominated Hillary Clinton for president during its convention in Philadelphia July 25 to 28. According to most major polls, she is in the lead over Republican candidate Donald Trump for the November 8 election.

“The index rose in late July because of the higher level of economic confidence that Democrats exhibited after the Democratic National Convention,” Gallup said in a statement. “By and large, Democrats have retained their higher confidence in the economy, which has kept the index stable for the last three weeks.”

Last week, all three major U.S. stock indexes reached record highs on the same day, the first time this has happened since the dot-com bubble of the 1990s. Gallup said the development “failed to energize Americans' confidence in the economy. In fact, the index's rolling average for the first three days after this development was a bit lower (-13) than averages recorded earlier in the week.”

Gallup's U.S. Economic Confidence Index is the average of two components: how Americans rate current economic conditions and whether they feel the economy is improving or getting worse. The index has a theoretical maximum of +100 if all Americans say the economy is doing well and improving, and a theoretical minimum of -100 if all Americans say the economy is doing poorly and getting worse.