How do Odds Develop for Repeated Women's Singles Matches?

These posts expand the analysis from the previous two posts on repeated matches. In the first post, we discussed the test-retest reliability of badminton matches. Then, in the second post, we saw what the most frequent line-ups are and how often the matches between these players were won by the same player or pair.

In this post, we will discuss some of the most frequent women’s singles line-ups. The other disciplines will have seperate posts.

Methodology

The methodology follows what was said in the post How do Odds Develop for Repeated Men’s Singles Matches?.

Tai Tzu Ying - Ratchanok Inthanon

We start with the line-up with the most matches. We see that until mid 2016, matches were between even odds and favouring Ratchanok with a win probability of 60%. Since the beginning of 2017 Tai Tzu Ying has been the 60-70% favorite. I don’t know what changed in 2016. The difference in the probabilities conforms the different outcomes, as Ratchanok won two matches during the first half of 2016 when her probability was large, then lost the next three matches when herprobability was lower. She won some matches at the end of 2018, which brought her implied win probability back to around 40%. Lately bookies and the match outcomes have been favoring Tai.

Tai Tzu Ying - Sung Ji Hyun

We see that Sung ji Hyun was a 60%-favorite until around the year 2016. Then the implied win probability for her fell to around 10% over the next years. I don’t know if this can be explained by her being 3 years older than Tai Tzu Ying. As a similar change can be seen in the plot for Tai Tzu Ying and Ratchanok Inthanon, we can assume that Tai massively improved during 2016. We also see that this decreased probability is supported by the loss of all matches since the beginning of 2017. In 2016 Sung still won three matches, but this didn’t suffice to convince bookies to give her a greater win probability.

Ratchanok Inthanon - Sung Ji Hyun

This plot shows similar characteristics as the one for Tai Tzu Ying and Sung Ji Hyun, although this one is not as pronounced. Sung had some successful matches in 2017 and 2018 which resulted in an increase of her win probability, but the general decrease is still visible. And I don’t know, why there is one match in 2012 that has Sung with a win probability of almost 75%, more than 10% more than the second highest value.

Pusarla Venkata Sindhu - Akane Yamaguchi

PV Sindhu is about two years older than Yamaguchi, so this might be one explanation for the general upward trend for Yamaguchi’s win probabilities. The matches in 2016 show a good example of the expected behaviour: in both matches PV Sindhu’s win probability increased after having won the previous match. Since the end of 2017, the wins are more evenly distributed and the implied probabilities scatter between 50 and 60% for Yamaguchi.

Tai Tzu Ying - Carolina Marin

Implied probabilities started slightly favoring Marin and rose to their maximum after four wins and only one defeat at the end of 2016. Then five wins for Tai Tzu Ying followed, driving the win probabilities in Tai Tzu Ying’s favour and leaving her as a 60%-favorite at the end of 2019. Since then, Marin could again win some matches and increase her win probability back to around 60%.

Conclusion

In these women’s singles line-ups we can see several long-term changes. First the downswing of Sung Ji Hyun during the last years, but also the changes of ratings between PV Sindhu, Akane Yamaguchi, Tai Tzu Ying and Carolina Marin.