{"id":3779,"date":"2019-11-28T16:43:48","date_gmt":"2019-11-28T16:43:48","guid":{"rendered":"http:\/\/www.tennisabstract.com\/blog\/?p=3779"},"modified":"2019-11-28T16:43:48","modified_gmt":"2019-11-28T16:43:48","slug":"the-likelihood-of-live-doubles-rubber-in-the-new-davis-cup","status":"publish","type":"post","link":"https:\/\/www.tennisabstract.com\/blog\/2019\/11\/28\/the-likelihood-of-live-doubles-rubber-in-the-new-davis-cup\/","title":{"rendered":"The Likelihood of Live Doubles Rubber in the New Davis Cup"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\">In the new Davis Cup Finals format, each country-versus-country tie consists of three matches: two singles and one doubles. The singles rubbers are played first, so it&#8217;s possible that the doubles rubber will be &#8220;dead&#8221;&#8211;irrelevant to the result of the tie. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The Davis Cup Finals organizers aimed to make the doubles matter more, by using tiebreakers (based on sets and games won) to determine which sides advance from the round-robin phase to the knock-out rounds. It may have helped keep dead doubles rubbers interesting at first, but by the final days of the round-robin stage, teams that automatically qualified for the knock-out rounds had no remaining incentive to play doubles. Canada gave the United States a walkover, and Australia retired after one game. This was probably inevitable, but it isn&#8217;t ideal. Fans would presumably prefer to watch more tennis, and unfinished matches could wreak havoc with the tiebreaker system.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">There are a lot of possible ways to restructure the event&#8211;so many that I&#8217;m not going to explore that topic today. Since dead doubles rubbers are inevitable, I&#8217;d instead like to look at how often we should expect them to occur and, given that they will occur, whether that truly sidelines doubles in comparison with singles.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Live doubles<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This topic was prompted by a question ahead of <a href=\"http:\/\/www.tennisabstract.com\/blog\/2019\/11\/25\/podcast-episode-78-the-davis-cup-finals\/\">this week&#8217;s podcast<\/a>:<\/p>\n\n\n\n<figure class=\"wp-block-embed-twitter wp-block-embed is-type-rich is-provider-twitter\"><div class=\"wp-block-embed__wrapper\">\n<blockquote class=\"twitter-tweet\" data-width=\"550\" data-dnt=\"true\"><p lang=\"en\" dir=\"ltr\">Please use Elo ratings of the four players in the two singles matches to work out how often the doubles is decisive.<\/p>&mdash; Luke Burrage (@lukeburrage) <a href=\"https:\/\/twitter.com\/lukeburrage\/status\/1198987446417006592?ref_src=twsrc%5Etfw\">November 25, 2019<\/a><\/blockquote><script async src=\"https:\/\/platform.twitter.com\/widgets.js\" charset=\"utf-8\"><\/script>\n<\/div><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">The most extreme way of handling dead doubles rubbers is simply not to play them. If we went that route, how many doubles matches would we see?<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">At the Davis Cup Finals last week, there were <a href=\"https:\/\/www.daviscup.com\/en\/draws-results\/finals\/2019.aspx\">25 ties<\/a>: 18 in the round-robin stage, and 7 knock-out ties. 12 of the 25 featured a live doubles rubber: 7 of the 18 round-robin ties, and 5 of the 7 knock-outs. Using Luke&#8217;s proposed methodology, that&#8217;s roughly what we&#8217;d expect. The average tie (across all stages) had a 43% chance of reaching a deciding doubles rubber, suggesting that 11 doubles matches would matter.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Here is a list of the 25 ties, along with the probability that the two sides would split the singles rubbers. I&#8217;ve also shown whether the doubles rubber turned out to be necessary. Elo ratings didn&#8217;t do a very good job predicting <em>which<\/em> ties would require a doubles decider, even though they do give us a good estimate of how often the doubles will make the difference.<\/p>\n\n\n\n<pre>Tie                  Decider Odds  Decider Actual  \nSemi: GBR vs ESP            56.2%             YES  \nQuarter: SRB vs RUS         54.3%             YES  \nSemi: RUS vs CAN            53.3%             YES  \nRR: FRA vs SRB              52.5%              NO  \nRR: ARG vs GER              51.6%              NO  \nRR: USA vs CAN              51.4%              NO  \nRR: ITA vs CAN              50.0%              NO  \nQuarter: GBR vs GER         50.0%              NO  \nRR: GBR vs KAZ              49.8%             YES  \nRR: ESP vs RUS              49.4%             YES  \nQuarter: AUS vs CAN         49.4%             YES  \nRR: USA vs ITA              48.7%             YES  \nRR: BEL vs AUS              46.1%              NO  \nRR: KAZ vs NED              46.0%             YES  \nRR: CRO vs RUS              45.7%              NO  \nRR: GER vs CHI              44.2%             YES  \nRR: ARG vs CHI              43.6%              NO  \nRR: FRA vs JPN              43.4%             YES  \nFinal: CAN vs ESP           40.8%              NO  \nRR: GBR vs NED              37.5%             YES  \nRR: BEL vs COL              36.2%              NO  \nQuarter: ARG vs ESP         34.6%             YES  \nRR: SRB vs JPN              26.1%              NO  \nRR: AUS vs COL              10.4%              NO  \nRR: CRO vs ESP               7.3%              NO<\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">Only a few ties were near-guarantees of a singles sweep. Even with a fairly deep 18-team draw, most countries were able to bring two solid singles players, while few sides featured more than one singles elite.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>A decade of context<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This wasn&#8217;t just a fluke. I went through all World Group ties (not including the Playoff round) from 2010-18, and identified the two best singles players who appeared on court for each side. Using their Elo ratings at the time of the contest for the new best-of-three-sets format, I estimated how often we would get a deciding doubles rubber.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Across those 135 ties, the average likelihood of a doubles decider was 41%, only a bit lower than the observed rate this year. Barring some radical shift in the geography of global tennis, that gives us a pretty good idea of how frequently we should expect to see a two-match singles sweep in the new Davis Cup format.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>How much does doubles matter?<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">When doubles matches are live, they are particularly important. Each singles rubber has a great deal of influence on each side&#8217;s chances of winning the three-match tie, but once the doubles rubber is in play, it has <em>all<\/em> the influence.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Think of this in terms of <em>leverage<\/em>, the concept I usually use for in-match shifts from one point or game to the next. Imagine two identical sides, and consider their chances of winning at each step of the process. Each side has a 50% chance of winning each rubber, which means:<\/p>\n\n\n\n<div class=\"wp-block-group\"><div class=\"wp-block-group__inner-container is-layout-flow wp-block-group-is-layout-flow\">\n<ul class=\"wp-block-list\"><li>Each side has a 50% chance of winning the tie.<\/li><li>Whichever side wins the first rubber will have a 75% chance of winning the tie.<\/li><li>If the two sides split the singles rubbers, each side will once again have a 50% chance of winning the tie.<\/li><\/ul>\n<\/div><\/div>\n\n\n\n<p class=\"wp-block-paragraph\">Now consider the leverage of each match from the perspective of the first side:<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li>If they win the first singles rubber, their chances of winning the tie improve to 75%. Otherwise, they fall to 25%. That&#8217;s a leverage value of 75% &#8211; 25% = 50%.<\/li><li>Assume they win the first singles rubber. If they win the second, they win the tie&#8211;a probability of 100%. If they lose, it falls to 50%. Again, that&#8217;s a leverage value of 100% &#8211; 50% = 50%. (If they lose the first rubber, the math is the same, just with probabilities of 50% and 0% instead of 100% and 50%.)<\/li><li>If there is a deciding doubles rubber, the pre-match probability of winning the tie is 50%. Win the doubles, and the likelihood increases to 100%; lose it, and the probability is 0%. That&#8217;s a leverage value of 100% &#8211; 0% = 100%.<\/li><\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Maybe you think this is excessively formal and long-winded, and you might be right. The point is, given two equal sides, <strong>the doubles is twice as important.<\/strong> Plenty of other sports have similar features in which certain players appear infrequently, but at key moments.  Consider baseball closers, who don&#8217;t pitch in every game, only appearing late in tight games. Or NFL kickers, who only take part in a handful of plays each game, but have the potential to score on many of them.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Theory and reality<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In the sample framework I&#8217;ve just laid out, the doubles rubber will be live exactly 50% of the time, and it is twice as important as each singles rubber. That isn&#8217;t exactly how it works out in real life, since the doubles rubber is only decisive a little more than 40% of the time. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Still, when the doubles rubber matters, it is always make-or-break&#8211;or, in my terms above, it has a leverage value of 100%.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">I&#8217;m happy to leave dead doubles rubbers unplayed. Doubles specialists might be unhappy with such a decision, and I fear the wrath of Davis Cup traditionalists. However, this way of thinking about what&#8217;s at stake might soften the blow. In a 16- to 18-team Davis Cup structure, the teams are typically balanced enough that the doubles rubber is necessary almost half the time. And when it is, the oft-unsung doubles specialists get to play a match that is&#8211;literally!&#8211;twice as important as each ratings-grabbing singles rubber.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>In the new Davis Cup Finals format, each country-versus-country tie consists of three matches: two singles and one doubles. The singles rubbers are played first, so it&#8217;s possible that the doubles rubber will be &#8220;dead&#8221;&#8211;irrelevant to the result of the tie. The Davis Cup Finals organizers aimed to make the doubles matter more, by using &hellip; <a href=\"https:\/\/www.tennisabstract.com\/blog\/2019\/11\/28\/the-likelihood-of-live-doubles-rubber-in-the-new-davis-cup\/\" class=\"more-link\">Continue reading <span class=\"screen-reader-text\">The Likelihood of Live Doubles Rubber in the New Davis Cup<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[27,31],"tags":[],"class_list":["post-3779","post","type-post","status-publish","format-standard","hentry","category-davis-cup","category-doubles"],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/www.tennisabstract.com\/blog\/wp-json\/wp\/v2\/posts\/3779","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.tennisabstract.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.tennisabstract.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.tennisabstract.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.tennisabstract.com\/blog\/wp-json\/wp\/v2\/comments?post=3779"}],"version-history":[{"count":0,"href":"https:\/\/www.tennisabstract.com\/blog\/wp-json\/wp\/v2\/posts\/3779\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.tennisabstract.com\/blog\/wp-json\/wp\/v2\/media?parent=3779"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.tennisabstract.com\/blog\/wp-json\/wp\/v2\/categories?post=3779"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.tennisabstract.com\/blog\/wp-json\/wp\/v2\/tags?post=3779"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}