When Jelena Jankovic becomes world No.1 next week, she’ll do it on the back of just one title – the Tier I (Masters level) event in Rome. Her next best results are two Grand Slam semi-finals and two other Tier I finals.

To make matters worse, Jankovic has back-pedaled her way to the summit, not even capturing a tournament while No.1 was on the line. A win in Los Angeles two weeks ago would have given her the top spot, but she lost in the semi-finals. It was the same scenario in Montreal last week, but she lost in the quarter-finals.

Jankovic managed to secure the position only because Ana Ivanovic and Svetlana Kuznetsova also lost early. So quietly did she slip in the back door that it took until the next day for the news to become official. After her loss on Friday, Jankovic was seemingly unaware that she still had a chance to shortly become No.1.

By Friday evening, all three of the top contenders were out of the event, and Jankovic’s imminent ascension was announced late the following afternoon.

Those who watch the sport often debate the quality of the No.1 player, and recently we’ve had more reason to do so. Much like the men’s succession of short-lived No.1s in the late 1990s, the women have been churning out a growing number of half-established No.1s – all fine players but without the pedigree of their dominant predecessors. Being No.1 doesn’t quite carry the same weight during such periods.

Jankovic is the most striking example ever of the latter group – the only player to achieve the top ranking without even having been to a Grand Slam final. It’s a new low all right, but the bar has been steadily dropping for some time.

Kim Clijsters made history in 2003 when she became the first player to rank No.1 without a Grand Slam title to her name, and Amelie Mauresmo soon followed suit in 2004.

By the objective measure of ranking points held when becoming No.1, it’s clear that the past four players to reach No.1 have been the least dominant of the decade – and in reality, the least dominant since rankings began in 1973.

But public perception of the top player’s legitimacy is often determined by the more subjective criteria of career achievement and the ability to defeat other top players.

Astonishingly, four of the past six new No.1s have not been holding a Grand Slam title when they reached the top ranking – Jankovic, Mauresmo, Clisters, and Maria Sharapova, who became No.1 just over a year after winning Wimbledon as a 17-year-old.

Even when Ivanovic clinched the top spot this June, she did so by winning her French Open semi-final – had she lost the final, she would still have moved up and become yet another Slamless No.1.

It used to be that you won Slams and then got to No.1. these days, players have been getting to get to No.1 and then – if all goes well – winning a Slam or two. What are the key reasons behind the trend?

1. Justine Henin's retirement

It’s a short-term aberration, but the sudden retirement of the world’s top player in May has had a very real and direct impact on the rankings. Even if Henin hadn’t played between her shock announcement and now, she would have stayed No.1 until the week after next.

Ironically, that's also when Jankovic is likely to drop back down to No.2 or No.3. So it's unequivocally true that, all else being equal, the Serb would not be No.1 next week had Henin not retired. Ivanovic would also still be waiting for a chance at the top spot.

2. More depth to the game

Ten years ago, a player who could hit solidly off both wings from the baseline could be assured of a reasonable future on the tour. Now there are scores of young Eastern Europeans and a smattering of canny veterans all capable of doing that and more, and top players are no longer blowing others off the court in match after match. As the Williams sisters demonstrated at the French Open, and Ivanovic and Sharapova at Wimbledon, even the early rounds of Grand Slams now bring players capable of knocking off a rusty top seed.

As a result, it’s hard for a single competitor to dominate the way Martina Navratilova, Steffi Graf, Monica Seles and even Martina Hingis did. Now, someone like Jankovic, who keeps piling up semi-finals and quarter-finals, can keep pace with the scattered up-and-down results of the big-time winners.

3. Injuries

Injuries have prevented most of the top players from playing a full schedule over the last few years, giving someone like the tireless Jankovic an even bigger edge in piling up ranking points. And a spate of retirements – Clijsters, Hingis, Henin, Myskina – have helped clear the way for younger players to move up.

4. The ranking system

In an effort to encourage players to play more, the WTA ranking system has increasingly rewarded quantity over quality. Points are now are calculated not by averaging a player’s total results but by adding together her best results. As a result, there’s no cost to playing extra events – losing in the first round would bring down your average under the old system, but under the new system you can simply drop your lowest score as long as you play more than 18 events.

Jankovic, who has played 23 events over the past year compared to 14 for Serena Williams and Sharapova, has much more padding in her points total than either of the two past Australian Open champions.

The benchmark for an average schedule has also increased from 12 events in 1995 to 14 in 1996 to 17 today. It is scheduled to drop back to 16 under next year’s Roadmap changes.

Finally, the decision two years ago to stop awarding extra points for defeating top players has shifted the emphasis away from quality and towards the sheer ability to notch wins (against anyone). The Roadmap will next year severely restrict where top players can play and should result in more match-ups between them, but it doesn’t offer any extra boost for rising youngsters or the tour’s giant-killers.

Like Clijsters and Mauresmo, who eventually backed up their No.1 spots with Grand Slam titles, Jankovic still has time to build a resume that will retroactively make her a fully-fledged member of the club. But during her reign next week, she'll have the dubious distinction of being the least accomplished No.1 in WTA history.