Before the Deadline

Iris had twenty minutes left before the deadline for her class project. She and Ben had counted the cyclists using the road outside their college. Their report argued that more people cycled on Mondays than on Fridays. Ben had already made a colourful chart, and Iris was checking the document before sending it.

Then she noticed the dates in their notebook. Their Monday count had lasted an hour, but on Friday they had only stayed for thirty minutes because of the rain. The chart compared the totals as though the two periods had been the same. It looked convincing, but it did not support their conclusion.

Ben suggested sending the report and explaining the problem if the teacher asked. Iris disagreed. “If we leave the chart like this, readers will think we measured the same thing,” she said. There was no time to collect new figures, so they would have to change what the report claimed.

They kept the original numbers but removed the sentence about Mondays being busier. Under the chart, Iris added a note explaining the different counting periods and the weather. Ben wrote that they would need several counts of equal length before making a comparison. They sent the project with two minutes to spare.

The next day, the teacher asked why their conclusion was shorter than their introduction. Iris explained the mistake. “Your result is limited,” the teacher said, “but you have told me exactly what those numbers can and cannot show.” On the way out, Ben opened a new notebook page. At the top he wrote: “Next time: check the method first.”