When it comes to working out which goalkicker is best, the simple way is to look at percentages.

The usual candidates in recent years have been at the top of the standings when it comes purely to percentages, South Sydney skipper Adam Reynolds, Panthers star Nathan Cleary and Canberra centre Jarrod Croker.

But if you factor in where each kick was taken over the past three years to come up with a True Kicker rating, it's former St George Illawarra captain Gareth Widdop who has been the NRL's sharpest shooter.

Under the True Kicker rating system, compiled by Stats Perform & Stats Insider for NRL.com, each attempt at goal is assigned a difficulty level based largely on where the kick is taken from on the field.

Players are then given a score for each kick based on the difficulty level of the kick, and whether or not the kick is successful. The score corresponds with how many "extra points" that particular kick earned their team compared to the NRL average kicking success rate from that particular location.

Scores for individual kicks can be positive (where the attempt is successful) or negative (where the attempt is unsuccessful) and range from +2 to -2.

This means a player who kicks a goal from the sideline will receive a higher score than a player who kicks a goal from right in front of the posts.

Similarly, a player who misses a kick from right in front will be penalised harder than a player who misses a kick from the sideline.

How is the difficulty of each kick calculated?

Using historical data, a benchmark is assigned to each kick that represents how often we would expect the NRL average kicker to kick a goal from that particular location.

Benchmarks typically become lower as the location of a kick moves away from the posts (in distance, and in angle from the goal). The lower the benchmark, the more difficult the attempt at goal.

How are True Kicker scores assigned for each kick?

If a kick is assigned a benchmark of 60%, that means we would expect the NRL average kicker to nail that kick 60 times if they were to have 100 shots.

If a player were to kick that particular goal, they would score +0.8 in the True Kicker Ratings, being the two points scored minus the average kicker’s expected points from that kick (2-0.8 = 1.2). Conversely, if a player were to miss that goal, they would score -1.2 (being the 0 points scored, minus the average kicker’s expected points from that kick) – a negative contribution to their team.

How can True Kicker ratings be used?

An overall leaderboard

A player’s "kick by kick" scores can be added together to produce an overall score which broadly represents how many extra points they have gained (or lost) for their team above (or below) the NRL average goal kicker.

A score of zero indicates a player has done exactly what we’d expect from the average kicker based on the kicks they have taken. A positive score indicates a player has done better than average.

Kick By Kick Ratings

A kick by kick, difficulty-adjusted-rating-system, allows us to calculate what we would expect a player’s goal kicking success rate (penalty goals and conversions) to be based on the kicks they have taken.

By comparing this to a player’s actual goal-kicking success rate we can calculate how much they have exceeded (or fallen below) expectation. This number is presented in the form of a percentage and represents how much better or worse a player’s conversion success rate is than we would expect it to be based on the kicks they have taken.

What does it all mean?

Over the past three seasons James Maloney (kicking success rate: 87.2%, +16.3pts on True Kicker Rating) and Nathan Cleary (kicking success rate: 86.8%, +22.4pts on True Kicker Rating) are the top two in terms of pure goal kicking success rate.

Widdop (kicking success rate: 83.3%, +33 pts on True Kicker rating) sits third for players with a minimum 60 kicks at goal. However, we can see Widdop overtakes them in both the overall True Kicker rating (three-year total) and per-kick True Kicker metrics.

This is driven by the difficulty level of kicks taken by all three players – of all kickers to have at least 60 shots at goal over the last three years, Maloney and Cleary have had the second and third easiest shots at goal, respectively.

So while the True Kicker ratings indicate they are both great goal kickers, their underlying success rate is somewhat inflated by the relative ease of the kicks they have attempted.

In recent times, a player such as Shaun Johnson has received criticism for his accuracy, particularly last season when Cronulla lost a record five matches when they scored more tries than their opponent.

However, the True Kicker ratings indicate he is quite a good kicker but over the last three years he’s had the second most difficult shots of all kickers to have taken at least 60 kicks, behind Gold Coast's Ash Taylor – making his 77% conversion success rate over the period actually quite impressive.

Canterbury legend Hazem El Masri is impressed by the array of talent among the modern-day kickers.

"There's a lot of quality kickers at the moment who I love watching kick," he said.

"Nathan Cleary and Adam Reynolds are kicking really well and probably stand out for me, every generation you set some standards and then new guys come in.

"They've got their own unique styles and it gets the fans going. I loved watching Joey Johns kick and James Maloney when he was still playing last year."

The views in this article do not necessarily express the opinions of the NRL, ARLC, NRL clubs or state associations.