The amount of money advertisers are spending on online ads has been dropping in recent years.

The average ad spend in November was $1.85 billion, down from $2.29 billion in 2010, according to research firm Quantcast.

The decline is largely driven by advertisers who are looking to increase sales and advertising efficiency, said Michael Nachman, director of digital marketing at Quantcast, a market research firm.

That’s led to fewer ads on mobile devices and in mobile video and social media, Nachma said.

But the trend isn’t entirely random.

According to Quantcast data, online advertising spending dropped last year by 2% and was expected to fall this year by 6%.

That’s partly because advertisers are paying less.

Nachman said online advertising has historically been more efficient, but the decline has accelerated in recent months.

That’s due to a series of changes that advertisers have made to their advertising strategies and tactics, including using artificial intelligence to target ads, and targeting audiences on mobile and other devices.

Natchman said the shift to using AI to target audiences is especially noticeable in video, which is used by more than $8 trillion in advertising each year.

Advertisers want to maximize their revenue potential, but there are also challenges to the way they reach people, Natchman added.

That includes getting people to click on ads and using technology to personalize ads to people based on interests.

While most advertisers are targeting ads to consumers who are interested in what they are looking for, Nachi said, they may be paying more to reach more people, which means they have less opportunity to generate revenue.

“There are a lot of companies that are going to lose money if we don’t have that much money to spend on advertising,” he said.