The Empty Split Column: Vietnamese Swimming and the Art of Hiding Data

Three in the morning in Nha Trang, and I am reopening the results file of a national swimming meet. The column I click first is always the splits column — the 50-metre breakdown. In most events, that column is empty. It is not that swimmers have no splits: everyone passes through the first 50 metres, the second 100, and the turns at the end of the lane. What is missing is the person who writes them down.

Numbers never lie, but they know how to hide. After twelve years at a spreadsheet, I believe the most dangerous thing in sport is not a bad metric but a metric that does not exist. When an indicator is missing, people default it to zero, and every conclusion built on top of it drifts.

Swimming has a feature that makes data-hiding easy. The final result is public: finish time, placing, medal. The structure of the swim — the chain of small decisions that produced that result — disappears the moment the official leaves the lane.

Context: three data sources, two of which do not exist

Swimming data in Vietnam comes from three places. The first is the organiser's report, which almost always contains only the final time and the placing. The second is the electronic timing system mounted at the pool, which holds splits and reaction times but is rarely released as open data. The third is video, and that is where I work: hand-timing every 50-metre segment, exactly the way I once built xG figures for the first twelve rounds of the 2026 V.League in Excel.

That manual method carries error, and I will not pretend otherwise. But an error of 0.2 seconds across a 50-metre segment still gives me what the report cannot: the shape of the race. A swimmer can win while closing 1.8 seconds slower than they opened, and that tells more about the next cycle than the medal does.

Internationally, World Aquatics publishes splits, reaction times and turn data for every lane at major meets. A coach in Budapest can know what percentage his athlete loses on the third turn. A coach in Vietnam, with the same athlete and the same race, usually knows only the total time. The gap between those two coaches is not expertise. It is access.

According to published results, Nguyen Thi Anh Vien won eight gold medals at the 2026 SEA Games in Singapore. At the Rio 2026 Olympics she placed ninth in the 400m individual medley heats, one position short of the final. From the same generation, Nguyen Huy Hoang took silver in the 1500m freestyle at the 2026 Asian Games in Jakarta.

My point is not the medals. Those two results are the biggest milestones in Vietnamese swimming in a decade, and to this day no complete set of splits has been published for either of them. In Huy Hoang's 1500m, we know how long he swam, but not how he held pace: did he lift at 800 metres and hold, or even-split the first three quarters and unload at 1,200? Those two strategies demand two entirely different conditioning plans for the next cycle.

Four layers of data that never reach the scoreboard

The first layer is start reaction and the opening 15 metres. In the 50-metre events, elite reaction times typically sit between 0.60 and 0.68 seconds. A tenth of a second at this layer is worth several places in a regional final. Vietnam publishes very little on reaction time, which means a 50-metre event is being judged by an indicator that does not measure the most decisive part of it.

The second layer is split structure. Over 200 and 400 metres, the question is not fast or slow but where the speed lives. A negative split — closing faster than opening — signals a conditioning base and the ability to distribute energy. An over-fast opening signals an immature race plan. Both are invisible if you read only the total.

The third layer is stroke rate and distance per stroke. Two swimmers can finish in the same time while one takes 44 strokes per minute over a short distance and the other takes 36 over a long one. The first is burning energy faster, and in the 400m individual medley that debt usually falls due in the breaststroke leg.

The fourth layer is pool context. Times from a 25-metre pool and a 50-metre pool cannot be compared directly; conversion factors exist but differ by event and by swimmer type. Add water temperature, altitude and the accuracy of the touch pad at the finish, and you get a paradox: swimming has the most precise measurement system in sport, and most of what it measures is never published.

One technical detail is rarely mentioned. In a relay leg, a swimmer starts from a flying position, so their leg time is roughly 0.6 to 0.7 seconds faster than a standing start. Comparing that figure directly with an individual personal best is methodologically wrong. A simple headline saying a relay leg was faster than the national individual record can be arithmetically correct and completely meaningless.

Competition structure: A standards, B standards and universality places

For Olympic qualification, World Aquatics sets two time standards, commonly called the A cut and the B cut, plus a small number of universality places for nations without a qualified swimmer. The difference between those two routes is enormous in data terms. A place earned through the A standard says the swimmer went faster than an absolute threshold. A universality place says the country has a representative, but nothing about the distance to that threshold.

In many season reviews, the two get merged into one line: qualified for the Olympics. For a reader, that is good news. For an analyst, they are two different states, sometimes three to five seconds apart over 400 metres. Merging them is the fastest way to lose the ability to measure progress across an entire cycle.

There is also a structural point. The SEA Games run on a two-year cycle, the Olympics on four, and whichever peak you choose determines the whole training plan. When the SEA Games is the highest target, athletes are tapered toward the region and the curve against the world stops being readable. That is a rational choice for medals, but it creates a data void during the exact years a swimmer develops fastest.

Read the curve, not the table

People look at the valuation table; I look at the curve. Many deals die before they are announced — and in swimming, many young talents vanish before anyone sees them, because nobody holds enough data to notice.

Take an example from my own dataset. A 200m breaststroke swimmer drops 1.2 seconds in twelve months. At that age, the average improvement slope for the cohort is around 0.4 seconds per year. A drop three times the baseline has two explanations: a genuine breakthrough, or a bubble. Separating them requires context data — did training volume rise, was the taper pushed early, was the swim in a 25-metre or a 50-metre pool, and was it the only result of the season.

Luck is something I do not have. I have probability and enough data. Before looking at any table, I set the threshold in advance. Hand timing carries plus or minus 0.3 seconds. Electronic timing carries plus or minus 0.01 seconds, but the touch pad can fail on a two-handed finish. So a national record 0.2 seconds under the old mark needs verification, while a 1.5-second gain over 200 metres is a signal. Setting the threshold after seeing the data is the surest way to turn noise into a story.

The counter-intuitive part: empty cells are not neutral

First, more data is not automatically better. Swimming has indicators that measure effort rather than efficiency, and they are as dangerous as distance covered in football. Weekly training volume, total stroke count, number of sessions — these are the easiest things to measure and the easiest to be misled by. A swimmer logging 60 kilometres a week with a short distance per stroke is accumulating two things at once: pretty data and a shoulder injury.

Second, an empty cell is not neutral. It has an owner. Whoever holds the splits holds the power to price an athlete, because they are the only party that knows where the curve sits. In football, small clubs survive by selling young players, and they can only sell when the buyer believes in the curve. In Vietnamese swimming, the buyers — foreign universities, regional training centres — usually have no splits, so they price on medals. And a SEA Games medal, standing alone without context, is discounted heavily.

Here is the paradox: Vietnamese swimming has one of the most accurate measurement systems in the region, mounted at the pool, running at every meet. Yet the economic value of that system is left on the floor, because nobody exports it as a shared data file.

In 2026, when pools closed and the whole industry waited, I reopened every junior meet report going back to 2026. No meet was meaningless — not even the one with four lanes, a single timekeeper and no spectators. In those rows I found the improvement slopes of athletes who later joined the national team, and of those who disappeared at seventeen. The difference between the groups was not in their first results. It was in the shape of the following 24 months.

Governance: where missing data becomes risk

There is one area where data gaps cause worse damage than a bad analysis: governance and anti-doping. The Athlete Biological Passport relies on longitudinal data — blood and steroid markers tracked over years. The thicker the baseline, the higher the chance of detecting anomalies, and the easier it is to protect a clean athlete from a false positive.

In countries with weak data systems, both sides lose. Athletes lose their own protective tool, authorities lose their reference, and technical disputes — a two-handed touch at the finish, a breach of the 15-metre underwater rule — get settled by testimony instead of a record. Where data is absent, argument fills the space.

Career cycle: a narrow window and the cost of two lost years

I have written about esports that player careers are shorter than footballers', while youth systems and post-retirement support are close to zero. Swimming shares one worrying trait: the peak window is very narrow. For women, the strongest years usually fall between 18 and 26; for men, between 20 and 30.

Inside a window that short, two years without split data are two years in which nobody knows whether an athlete is rising or stalling. A footballer can have two quiet seasons and still hold transfer value, because the career is long. A swimmer's two quiet seasons can be the entire peak of a career.

The ripple chain: from a local pool to a scholarship

Swimming's ripple chain is longer than most people assume: local pools produce athletes, training centres filter them, the national meet produces medals, media produces image, and sponsorship and scholarships flow back to the local pool. Weak data at the first link blocks the whole chain.

Without public splits, media can only write about medals, and a medal story runs dry in three days. A sport with no curve to tell has no season to sell. This is not swimming's problem alone; it is the lesson domestic football already went through, and the way out was turning data into a public product.

Signals for the next cycle

I am not proposing a complex system. Three rows of data would be enough to change how Vietnamese swimming is evaluated over the next twelve months. First, 50-metre splits for every national final, published within 48 hours of the pool closing. Second, reaction times and turn data, which already exist inside the timing system. Third, a mandatory note beside every result stating whether it came from a 25-metre or a 50-metre pool.

The cost of those three rows is close to zero, because the infrastructure already exists. The only thing that needs to change is habit: treating data as a product of the meet rather than the private property of a coaching staff.

I do not need another medal to believe in the future of Vietnamese swimming. I need one more column of numbers. When that column is filled, I will be the first to say that some of my old conclusions were wrong — and that will be the only proof that this dataset is alive.