Fourteen for 206. Those were the combined figures of Tim Southee and Trent Boult as they ripped out India's celebrated batting line-up to hand New Zealand a convincing victory in Wellington. The numbers would have been particularly satisfying because both bowlers were coming back from a bit of a low: Boult was returning from injury, while Southee was less than impressive in white-ball cricket just before the Tests. These returns, though, underscored just how vital they are to New Zealand's fortunes in red-ball cricket. As a bowling combination, they rival some of the greatest new-ball pairs in Test cricket.

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In innings when the two bowlers have shared the first new ball, Boult and Southee have combined to take a total of 426 wickets, which is third in the all-time list. The only pairs with a higher tally are James Anderson-Stuart Broad and Wasim Akram-Waqar Younis. Before the Wellington Test, the New Zealand dup was level with Curtly Ambrose and Courtney Walsh on 412 wickets, but now they are well clear of the West Indian pair, with their next target just 50 wickets away.

The Boult-Southee combination is also remarkable because of how closely matched their numbers are: out of these 426 wickets, Boult has contributed 214 at 26.25, compared to Southee's 212 at 26.77. There is hardly anything to separate the two, as is the case with their overall numbers.

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The Wellington returns would also be gratifying to the pair because their recent stats hadn't been so hot. In the last five Tests they had played together before this one, they had tallied 33 wickets for 1017 runs - that's an average of 6.5 wickets per Test, and nearly 31 runs per wicket. Against India, though, they were back at their best, especially after Boult shook off his post-injury rust in the second innings. The combined haul of 14 for 206 is their fifth-best, in the 54 Tests they have played together. In fact, they were only one wicket away from equalling their best tally in a game.

Five of their top six combined hauls in a Test (and 11 of their top 13) have come in home conditions, which isn't a surprise given that both are primarily swing bowlers who don't have extreme pace. What they do have in abundance, though, is the ability to swing the ball both ways and exploit favourable conditions. In innings when they have shared the first new ball in home conditions, Boult and Southee have a combined tally of 256 wickets at an average of 24.3. [Individually, again, the numbers are similar for the two: 131 wickets at 23.96 for Boult, and 125 at 24.65 for Southee.]

Over the eight-and-a-half years that Boult and Southee have been playing together, New Zealand's Test results have been significantly better in matches where both have played, compared to matches where either one - or neither - has played. The table below lists out those three situations: when both have played, New Zealand have a 28-15 win-loss record; when one of the two has played, it reduces to 3-9; in the five Tests neither has played, New Zealand have lost three and drawn two.

Combining the instances when only one of the two bowlers played a Test or when neither of them were in the XI (since they first started playing together), New Zealand have a 3-12 record in 21 Tests. Compare that with their 28-15 win-loss record when they have both played, and it's obvious that the difference is huge. The impact value of 7.46 is obtained by dividing the win-loss ratio when both played (1.87) with the ratio in the other 21 Tests (0.25). This value indicates that New Zealand's Test results have shown a seven-fold improvement when both Boult and Southee have been a part of the team.

Impact factor = (Ratio playing together)/ (Ratio not playing together) ESPNcricinfo Ltd

Obviously, that doesn't mean that the entire difference can be attributed to Boult and Southee. There are other factors involved, including the performances of the batsmen and the other bowlers. Plus, Boult and Southee tend to play more often than not in home games, where conditions are generally in favour of New Zealand. [At home, New Zealand have an 18-2 record with these two playing, and 2-2 otherwise; in away and neutral venues, the corresponding numbers are 10-13 and 1-10.]

The numbers above do say that New Zealand's results lift considerably when Boult and Southee are in the XI. Comparing that impact value with other pairs of bowlers (those with at least 300 wickets playing together for their country, with each bowler contributing at least 40%, and with at least 10 Tests during their career span when they didn't play together), only one pair - R Ashwin and Ravindra Jadeja - have a bigger difference in win-loss ratios. That is because they tend to play together at home, where conditions are generally spin-friendly; overseas, only one of them typically plays. Compared to everyone else, though, Boult and Southee seem to have had a greater impact on team results, which indicates just how vital they have been to New Zealand's Test fortunes.

Stats inputs by Shiva Jayaraman. Graphics by TS Girish