China’s economic data have always been fraught. Now, all eyes are on the coronavirus numbers, which economists and investors are using to estimate the outbreak’s toll—and they are too perfect to mean much.

A statistical analysis of China’s coronavirus casualty data shows a near-perfect prediction model that data analysts say isn’t likely to naturally occur, casting doubt over the reliability of the numbers being reported to the World Health Organization. That’s aside from news on Thursday that health officials in the epicenter...