The hammer rang once. A spark jumped off the anvil and did not go out. It waited. They followed.

The last issue of the Green Gazette that Tara would edit came out at the end of August, a week before she left. It had a black-and-white photograph of the whole Gazette team on the back page, squinting into the sun on the bench by the café, and a note from Mrs Hallam thanking them. It also had the paper's year-end awards, which had been Tara's idea in September and which she had nearly forgotten about until the last minute.

There were ten of them. Best New Shop. Best Dog of the Green. Most Helpful Neighbour. And, at the bottom of the page, the one Ollie had wanted to write because he took the bus every day:

MOST IMPROVED: ROUTE 7

Ollie had got the figures from the bus company's own website, which published how many of each route's buses had arrived on time every month. Route 7 ran from the Green to the hospital and back, and in March it had been terrible. Only sixty-one per cent of buses had arrived on time. People had been late for work, and late for appointments, and the Gazette had printed a furious letter from Mr Pettit about standing in the rain.

At the end of March, the bus company had moved the depot manager, Mr Dunn, to another depot across the county, and a new manager, Ms Kowalski, had started on the first of April.

And in April, Route 7 had been on time eighty-four per cent of the time.

From worst to best in a single month! Ollie had written. Ms Kowalski's new rotas have transformed Route 7. Passengers on the Green have a lot to thank her for.

There was a photograph of Ms Kowalski shaking hands with a driver.

On the first Monday after the issue came out, there was a letter in the Gazette box. It was typed, and signed in neat blue ink.

Dear Editor, it said. I was the manager at the depot until the end of March. I am happy where I am now, and I wish Ms Kowalski well. But I have been told by three of my old drivers that people on the Green now think I was the reason Route 7 was so bad, because your paper says it got better the moment I left. I would like to ask whether your reporter looked at the rest of the year. Yours sincerely, G. Dunn.

Tara pinned it to the board above the back table at the Whetstone café. She read it twice.

It was the last letter she would pin there. She had been proud of the last issue. Now she was uneasy. She did not know why yet.

"I was going to say the figures are the bus company's own," Tara said.

She had brought the letter to the back table. Danya was there, with a bus timetable he had picked up for no reason except that he liked timetables. Across from him sat Sofia, who kept every score of the school basketball team in a notebook and was fonder of a long list of numbers than of almost anything else.

"I was going to say it like this," said Tara. "Ollie didn't make anything up. He took the numbers from the bus company's website. Sixty-one in March. Eighty-four in April. That's a huge jump. Twenty-three points. He even checked them again yesterday, after the letter. I can write back to Mr Dunn and tell him the figures are official."

She had the sentence half written. Thank you for your letter. Our figures were taken directly from the operator's published data.

It felt good. It felt like the last solid thing she would do as editor: stand by a number from an official website.

Sofia read the award, and then the letter, and then the award again.

"Look at the whole season, not one game," said Sofia. "Two months is two games. Where's the rest of the year?"

"Hm. It's on the website," said Tara. "But the award's about March and April."

"Write all twelve down first," said Sofia. "Or as many as there are. Then we'll know what March and April mean."

"Says who the other months matter?" said Danya. "The award's for improving. It improved."

"Nobody says it," said Sofia. "That's what Mr Dunn's asking. Nobody looked."

Tara looked at the letter. Whether your reporter looked at the rest of the year.

"How do we know what Route 7 is usually like?" Danya asked.

Nobody knew. That was the problem.

Sofia found the figures on the bus company's website on her phone, and wrote them into her notebook in a long column, one month to a line, the way she wrote basketball scores.

September: 79%. October: 81%. November: 78%. December: 80%. January: 82%. February: 79%. March: 61%. April: 84%. May: 80%. June: 81%. July: 79%.

Then she drew a line down the side, from the top to the bottom, and looked at it.

"There," she said. "This is Route 7's season."

Tara looked at the column. Most of the numbers were nearly the same. Seventy-nine, eighty-one, seventy-eight, eighty, eighty-two, seventy-nine. Up a bit, down a bit, always about eighty.

And then March. Sixty-one. Sticking out of the column like a missing tooth.

"Every team has a spread, and Route 7 is usually about eighty per cent," said Sofia. "From September to February, the average is just under eighty. Seventy-nine point eight. Then one really bad month."

"And then April was eighty-four," said Tara. "That's better than usual."

"A bit better," said Sofia. "Four points above usual. It's had months like that before. January was eighty-two." She tapped the column. "But look at May, June and July."

Tara looked. Eighty. Eighty-one. Seventy-nine.

"Back to usual," said Sofia. "A very bad day is usually followed by a more ordinary one. That's all April is. The average is only half the story. The other half is how far a month can wander by itself."

She felt something shift, the way it had in the summer special with the pools, and in July with the blueberries. It was the feeling of a true number turning out to be standing on the wrong ground. It was a strange feeling to have on her last day.

Kiran was a point guard on the school team who also took maths very seriously, and he was honest even when it made him uncomfortable. He read Sofia's column and then the award.

"I'm not saying she's wrong," said Kiran. "I'm saying we can't tell yet. Moving together isn't the same as causing. Ms Kowalski started in April, and April was good. But what else changed between those games?"

"Between March and April?"

"What else changed? Something made March so bad," said Kiran. "Sixty-one is a lot worse than usual. What happened in March?"

Danya, who liked timetables, already knew.

"The roadworks," he said. "On the ring road, by the hospital roundabout. They closed two lanes for the whole of March. Route 7 goes round that roundabout four times every trip. They finished on the twenty-eighth. There was a sign."

Kiran nodded slowly.

"So in March, the buses were stuck in roadworks," he said. "And at the end of March the roadworks stopped, and at the end of March Mr Dunn left, and at the start of April Ms Kowalski came. Three things changed in the same week. It happened after, not because. April got better after she arrived. That doesn't tell us it got better because she arrived."

"Says who she did anything, then?" said Danya.

"Show me the games where he didn't yell," said Kiran. "That's what I'd say about a coach. Here it's: show me the months without roadworks. Before her, without roadworks, it was about eighty. After her, it's about eighty. If she made it better, it's not showing in the usual months yet."

"That's not fair. Not on her either," said Danya.

"No," said Kiran. "I'm not saying she's wrong. I'm saying we can't tell from this."

Yara ran the science fair and loved a coin toss, and was impossible to argue round. She had been reading over Kiran's shoulder.

"A fair test, or it's just a story," said Yara. "And this one isn't fair. Do you know why?"

"Can I say one thing? Because of the roadworks," said Tara.

"Partly," said Yara. "But even without the roadworks, it would still be unfair. Look at how the award was chosen. Which month did you start measuring from?"

"March," said Tara. "The worst one."

"If you choose when to do it, you've already biased it," said Yara. "If you start measuring from the worst month of the year, the next month will nearly always look better. Not because of anything anyone did. Just because the worst month is, by definition, worse than usual, and the next one is probably usual." She took a coin out of her pocket and spun it on the table. "Imagine you toss a coin ten times and get two heads. Very unlucky. Toss it ten more times. You'll probably get about five. Did the coin improve?"

"No," said Danya.

"Did anyone coach it?"

"No."

"That's April," said Yara. "Let chance pick, then compare. The fair test is the usual against the usual. Before the change, about eighty. After the change, about eighty. That's the comparison. And on that, Route 7 didn't improve. It went back."

Tara wrote it on her pad. Fair test: usual v usual. 80 v 80.

"Hm," said Tara.

Attest came last, with the Gazette's red pen. Attest had subbed every story that year and drawn a red circle round every claim without a name next to it. The year-end awards had come back with one red circle, round the words from worst to best in a single month. Next to it Attest had written: compared with which months?

"Who says so? I wrote it," said Attest. "And then it was the last issue, and everyone was signing cards, and I let it go."

"I saw it," said Tara. "I thought you meant it was too dramatic."

"Who says so, I meant. Which months," said Attest. "But nobody asked. Until Sofia wrote them all down."

"Let me listen first," Tara said, before anyone could start telling her what to write.

She took her pad and wrote three headings across the top, the way she had done eleven times that year: what we printed, what the whole year says, what we can't know.

Under the first she wrote worst to best; Ms Kowalski transformed it. Under the second, usually about 80; March was 61 (roadworks); after the change, about 80 again. The third column: whether her rotas helped at all, then whether Mr Dunn could have done anything about March, then what next year will look like.

"Hm. So what does a clarification like this have to carry?" Tara asked.

"Every claim names its source," said Attest. "The bus company's figures, all of them, not just two. That March was unusually bad, and that the ring-road works ended the same week. That the usual before and after the change is about the same. And that a very bad month is usually followed by a more ordinary one, whoever is in charge."

"Do we take the award away?"

"Put a name next to it. That's my bit," said Attest. "A correction names its source. What you do with the award is your call."

"Hm. That's a lot for one box," said Tara.

"A correction names its source too. It's your last one," said Attest. "Make it a good one."

Tara looked at Mr Dunn's letter again. People on the Green now think I was the reason.

"I think we missed someone," Tara said slowly. "Mr Dunn. We didn't just give her the credit. We gave him the blame. Nobody wrote that down, but everyone read it. If the box only talks about her, it still says he was the problem."

Nobody answered at once.

Mrs Hallam came in at four, for the last time that year. Ollie came with her, carrying the box of leftover last issues. Ms Kowalski came at quarter past, in her bus company jacket, straight from the depot. Mr Pettit came at half past, on his 1978 bicycle, because he had heard there was going to be a discussion about buses and did not want to miss it. Mr Dunn came last. He had driven forty minutes from the other depot, and he stood by the door until Mrs Hallam told him to sit down.

Ollie spoke first.

"I copied the figures exactly," he said. "Sixty-one and eighty-four. From their own website. It did go from the worst month to the best month. That's true. I didn't say anything that wasn't in the numbers. People wanted to know the buses were better, and they were."

It was the strongest version of his argument, and every number in it was true.

Ms Kowalski spoke next.

"I did change the rotas," she said. "In my first week. The drivers used to do split shifts, and now they don't, and they say they're less tired. That's real. I'm not claiming the roadworks. But I didn't do nothing, either." She looked at Sofia's column. "Though I'll be honest. I've looked at those numbers too, and I wondered why May wasn't better than April."

That was true too.

Mr Pettit cleared his throat.

"I would like it noted," he said, "that my bus has been on time every morning since April. Before that I stood in the rain for twenty minutes on fourteen separate occasions. I wrote to you about it. I am grateful to someone. I do not much mind who."

Then Mr Dunn spoke, quietly.

"I knew March would be bad," he said. "I wrote to head office about the roadworks in February. I asked for extra buses. They said no. Then March happened, and I was moved, and I never minded the move. I minded my old drivers telling me people think I wrecked a route for a year." He looked at the column of numbers. "Seventy-nine, eighty-one, seventy-eight, eighty, eighty-two, seventy-nine. That was my year. It was a normal year. With one bad month in it."

Nobody said anything for a while.

"Who checked that?" said Danya, very quietly. "Before we printed it."

Mrs Hallam took the corrections box out of her bag. It was the small grey panel at the bottom of page two, with a border round it and room for a few lines. She had used it twelve times that year, and every time she had set it in front of Tara. She set it there now, beside the last issue, with the photograph of the whole team squinting into the sun.

On the table in front of Tara was the last issue, open at the awards, with MOST IMPROVED: ROUTE 7 and a photograph of a handshake. There was Sofia's column, eleven months long, with one missing tooth in it. There was Danya's timetable, with ring road closed pencilled in the margin. There was Kiran's question, what else changed?, and Yara's coin, still lying where it had stopped spinning, and Attest's red circle, compared with which months? There was Ms Kowalski in her bus company jacket, and Mr Pettit, grateful, and a man who had driven forty minutes and stood by the door.

"You're the editor," said Mrs Hallam. "One last time. What does it say?"

She handed Tara the pen.

Tara looked at the empty box.

 

 

(Write the clarification Tara prints under the year-end awards.)

 

The spark dimmed to a warm dot and settled back on the anvil. The Green was just the Green again.

Back on the Green

That evening Lan, who was seven, got two out of ten in her spelling test, which had never happened before. Her teacher had given her a gold star sticker to cheer her up.

The next week she got seven out of ten.

She told Danya that gold stars made you better at spelling.

Danya asked her what she usually got.

Lan thought. She said usually about seven. The two had been the day she had a cold and couldn't hear the words.

She kept the gold star anyway. She said it was a good star, even if it hadn't done the spelling.

Afterword. The idea in this case is regression to the mean: when a result is unusually bad, or unusually good, the next one is usually closer to normal, whatever anyone does. Extreme results are partly luck, and luck rarely repeats. This makes it easy to give credit or blame that is not deserved. Start measuring from the worst month, and the next month will look like improvement; praise someone after their best day, and their next day will look like a decline. Before deciding that a change worked, look at the whole season, find the usual level before and after, ask what else changed at the same time, and compare the usual with the usual. You can practise looking at the spread, not just one result, in InferForge.