LOS ANGELES - When is the year’s best-selling album not the year’s best-selling album? When it’s by Taylor Swift. The star outsold every other artist in the US last year - shifting 1.9 million copies of her fifth record, Reputation, in just seven weeks.

But her decision to withhold it from streaming services until December damaged its chances in the chart of 2017’s most popular albums.

That’s because 1,500 streams now count as the equivalent of one album sale.

Swift accumulated 280,000 “streaming equivalent albums” in the four weeks Reputation was available on Spotify, Apple Music, Tidal and other services. But that wasn’t enough to put her ahead of Kendrick Lamar and Ed Sheeran.

Sheeran’s chart behemoth ÷ (Divide) was the year’s most popular album overall, according to Nielsen Music, which compiles the US charts for Billboard magazine.

The star accumulated 2,764,000 “equivalent album units” - a measure which combines pure sales, streaming equivalent albums and track equivalent albums (where 10 individual downloads count as one album). Compton-born rapper Lamar took third place, with his fiery, multi-Grammy-nominated album, DAMN.

Divide, which was released in March, has spent 43 consecutive weeks in the US top 20, and was also the UK’s most popular album on every available format - CD, vinyl, downloads and streaming.

A total of 169.15 million albums were sold in the US last year - down from 205.54 million in 2016.

But some formats bucked the trend. Vinyl sales rose for the 12th consecutive year, as fans bought 14.32 million LPs. The most popular album on vinyl was the Guardians of the Galaxy: Awesome Mix Vol. 1 with 64,175 sales. Surprisingly, cassette sales also shot up - from 42,098 in 2016 to 99,393 in 2017, according to BuzzAngle music.

People streamed twice as many songs every day (1.67 billion on average) as they downloaded across the entire year (563.7 million).

Despacito became the first ever song to break the one billion-stream mark in the US - racking up 1.1 billion streams on video and audio platforms.

But Kendrick Lamar’s Humble beat the Spanish-language hit on audio-streaming services, with 555.2 million streams over the year.

Almost one in five US adults (19%) now pay for a streaming subscription, according to BuzzAngle Music. He might not have released a proper album in 2017 (More Life was billed as a “playlist”) but Drake was the most-streamed artist for a second year in a row. The Canadian star achieved more than 6 billion streams - putting him far ahead of his closest competitor, Future, who had 4.2 billion streams. According to BuzzAngle, the top 10% of songs on streaming services accounted for 99.2% of all listening. Or, in other words, 90% of all the songs on Spotify and Apple Music were hardly ever played.

Rock music represented the largest share of album purchases in the US last year: an impressive 34.6% across all formats, and 54% of vinyl sales.

Once streaming was taken into account, however, rock’s market share dropped to 22%.

The younger audience who dominate streaming tend to choose urban and pop music over rock. Of the top 1,000 most-streamed songs of 2017, 50% were classified as urban music.

Ed Sheeran’s Shape of You dominated the US airwaves - spending 12 weeks as the most-played song on the airwaves, the longest run at number one since Uptown Funk.

According to Nielsen, the song collected 5.8 billion audience impressions, ahead of the second most-heard track of the year, Bruno Mars’s That’s What I Like, with 4.5 billion impressions.