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How did formats grow into the ones we know today? Some of those answers are found in some long-unseen national format computations done between the late ‘80s and the early ‘00s when Billboard and its radio trade publication, Airplay Monitor, teamed with the then-Arbitron to develop national format ratings.

Arbitron asked Billboard, beginning in spring 1989, to classify the stations in its nearly 100 continuous measurement markets for the purpose of creating national format ratings. The third party arrangement kept Arbitron from having to wade into controversies about how stations self-reported their format. Those most notably included the R&B/Hip-Hop stations that wanted to be known as Rhythmic CHR for sales or reporting status reason, but also more mundane cases like those stations that reported to the CHR chart but reported to the trades as the more adult-demo friendly Hot AC.

There were other differences. The national numbers were averaged from 12-plus numbers in nearly Arbitron’s continuously measured markets, roughly paralleling the top 100 markets. (Arbitron’s current numbers are based either on the smaller number of PPM markets, or on all markets.) Also, only commercial stations were included in the computations at the time. The original Billboard/Airplay Monitor stories are largely out of print now, although a few can be found online.

During the ‘90s, format rankings changed mostly glacially. It was easy to track the national shares of a format with the perceived strength of the available music, the growth in number of stations, and even certain format changes in the very largest markets. The loss of a Country station or the addition of a second Urban in New York often had a visible impact on national numbers because of the amount of available listening in the top markets. While diary methodology informed the ‘90s format trends, the gradual rollout of PPM from market-to-market became a variable unto itself.

Here’s how the formats trended in three year intervals between 1989 and 2001. All numbers are based on year-long averages, although numbers were provided quarterly. In part two of this series, we’ll look at how formats stack up against their current.

Adult Contemporary/Hot AC/Modern AC – AC began the ‘90s as America’s most listened to format. Its numbers benefit here from the combination of Hot AC and mainstream AC, but also from the sheer number of AC stations that existed at the time, typically several in a market. The station ranks swelled in the early ‘90s with the implosion of Top 40. AC peaked at an 18.7 share in summer ’90 and didn’t drop to the 13s until the Top 40 rebound in 1999. If you had broken out Hot and Mainstream AC, the latter would have accounted for most of the numbers, with Hot AC around a 4.5-5.0 share in the late ‘90s/early ‘00s.

Album/Active Rock, Alternative Rock– We think of heritage AOR stations as having imploded immediately as a result of the “new rock revolution” that grunge unleashed at radio, but Alternative’s building boom actually took place over the course of several years. In 1991-92, traditional AOR was still the only place to hear Alice In Chains and Pearl Jam in many markets. The format peaked at a 10.2 share in the summer of ’91. Alternative, meanwhile, began as barely measurable and peaked at a 4.4 in winter ’96, before the arrival of Modern AC splintered the format’s one-time Jewel-to-Tool coalition.

Classic Rock – It sat in the 3-share range throughout the first half of the ‘90s, then edged into the four-share range in summer ’96. Classic Rock cracked a five-share in summer ’99 and a six-share in spring ’01, only then passing the rock format from which it was splintered. Classic Rock’s mid-‘90s growth was also powered by grunge—as Alternative stations popped up in many markets, many heritage rock stations that bordered on Classic Rock chose to complete the transition. It received a further boost in the late ‘90s as those remaining AOR stations followed the music and morphed to the harder Active Rock format.

Country – There was already industry excitement about Country radio when the national numbers began in 1989, but the format didn’t really turbo until fall ’90 with the success of Garth Brooks and his colleagues. Buoyed by the rapid growth of new stations that expanded the audience, as well as the declines at mainstream top 40, Country went from a 9.5 share in spring ’90 to its 13.3 share peak in fall ’92. Even then, the format continued to grow in teens, reaching a once unimaginable 10.2 share in spring ’94. Country falls below a 10-share in winter ’98, at a time when consolidation was decreasing the number of available stations, as well as steering the format in an older direction for a while.

News/Talk/Sports – It took until fall ’94 for spoken word formats to surpass AC as the most-listened to format. But the format’s growth, driven by a proliferation of syndicated content, including Rush Limbaugh, that also made the once-cost-prohibitive format tenable for smaller stations and multiple stations in a market, was clear throughout the early ‘90s. The fall ’92 election book saw N/T up 14.0-15.2 with a 15.2-16.0 jump in the fall ’94 election book that is often thought to demonstrate the peak of Limbaugh’s powers. Spoken word formats peaked at a 20.7 share in fall ’99, but were still leading with a 17.3 share in late 2001.

Oldies – In 1989, the building boom for Oldies on FM was already a few years old. The format, also often represented by more than one station in some markets, remained fairly steady until 1994 when it peaked at a 7.7 share. Oldies started to taper off around 1997, in part because of the advent of Jammin’ Oldies, which siphoned off about a share (and which we counted at the time as part of the R&B world). In the early ‘00s, the format was showing just a little of the wear that would eventually spark concerns about a diminishing formula and an aging audience, driving a format exodus in the mid-‘00s that only ended with the arrival of PPM.

Mainstream/Rhythmic Top 40 – CHR’s previous peak is remembered as the mid-‘80s, but when the national numbers debuted, CHR trailed only AC among all formats. It then began a steady decline that saw the format fall into single digits in 1993, just as Country was peaking. Although Top 40’s musical rebound was clear as soon as 1996, we now forget that stations were still leaving the Top 40, which was expected to be primarily a niche youth format, powered only by a few broadcasters with enough stations in a given market to earmark one for 12-24 listeners. Top 40 doesn’t return to double digits until the peak of the boy band boom, winter ’00.

Urban/Urban AC – Buoyed by the additional listening that the then-new Urban AC format created, Urban radio showed steady growth in 1989-90, then sprung into double-digits in winter ’96, even amidst Top 40’s resurgence. The mid-‘90s driver was the growth of Hip-Hop and R&B stations, such as WQHT (Hot 97) New York, not all of which self-reported as Urban. When Urban finally became the largest music format in 2001, it was driven by the addition of Jammin’ Oldies to the format community, as well as a continued building boom that brought up to four urban stations of some variety into many large markets.

Spanish – Language Radio was a major ‘90s success story, moving into the 4-share range with the arrival of the Regional Mexican format on FM in the early ‘90s and into the 6s as Spanish AC stations grew in the mid-‘90s. By the end of the measurement period seen here, with the U.S. population shifting, Spanish-language radio controlled more than seven shares of listening and was still growing stations.

The success of Urban and Spanish radio in the ‘90s shows a clear arc, based on the available music, changes in programming, the growth of available stations, and the surrounding format landscape. When those formats were diminished in the initial Arbitron PPM results in the late ‘00s, the diary numbers were often dismissed by format outsiders as exaggerated—a vote for those formats on general principle by their biggest fans. But the dynamic growth of the formats in response to clear stimuli suggests otherwise.

In part II of this article, we’ll look at how ‘90s formats stack up against Nielsen’s current ratings.