# NRL Tips – Round 1, 2019

### But first, a refresher

This year I’m going to be providing tips for each round of the NRL and the ISC using four mathematical rating systems. None of the four metrics rely on subjective human assessments and instead, each rating system takes in cold, hard numbers and spits out tips.

While each tool has a useful predictive track record (some are better than others), they are unlikely to outperform the best human tipsters. However, the systems are also not subject to the cognitive biases that people naturally develop and can offer insights that might otherwise be overlooked.

The four rating systems are:

• Archimedes is an Elo rating system that tracks the form, or short-term performance, of NRL teams. The average rating is 1500, with the best teams typically 100 to 150 points or more above this mark. Archimedes ratings typically correspond to around six to eight weeks of results. Using this and accounting for home ground advantage, we can estimate each team’s winning probability.
• Eratosthenes is an Elo rating system that tracks the class, or long-term performance, of NRL teams. Like Archimedes, the average rating is 1500 with good teams being 100 or more above and bad ones being 100 or more below, but unlike Archimedes, Eratosthenes ratings track to approximately three years’ worth of results. You can read more about the differences between the systems here.
• Poseidon is a system that uses each team’s average rate of try scoring and conceding to estimate an expected score and calculate a winning probability. For these tips, we are using the simple calculation method described here.
• xPPG, unlike the other systems which are oblivious to personnel, looks at the Tuesday team list to assess which team has the stronger squad on paper. This is to account for the absence or inclusion of stars or poorly performing players in assessing each team’s chances. You can read more how PPG works here.

I refer to the four rating systems collectively as “The Jury”. Each system registers one vote, with the majority carrying the tip. Together, the Jury has a better track record than the individual rating systems on their own.

Embed from Getty Images

The Elo rating systems have been tried and tested over the last few years but Poseidon and xPPG are new for this season. While I’ve tested their predictive capabilities, I’m using them for the first time as analytical tools, so we’ll be learning about them together.

In the interests of transparency, I’ll be noting the success (and failure) of each system on the tip sheets.

Also bear in mind that as we are in the early part of the season, it takes time for each tool to dial in to the conditions of a new season. We can therefore expect the first few rounds to offer some dud tips until the rating systems get up to speed.

Here are the tips for this weekend’s action:

### National Rugby League

Correction: Blake Green is included in the named line up for the Warriors. This does not change anything in the sheet other than deleting the words “Green and” in my hot take and reducing “big outs” from the plural to singular.