An industries officer studied the fifty small units that have worked without a break for twenty years in the district's industrial estate and found that forty-six of them had never taken a loan. He concludes that keeping clear of borrowing is what keeps a small unit alive. Which of the following, if true, most weakens the officer's conclusion?

A habit said to keep units alive must be commoner among those that lived than among those that died, and the officer has looked only at the living. If the units that closed were just as free of borrowing, the habit divides nobody from nobody and the forty-six merely tell us that few units in the estate borrow at all. A change of ownership in two units, the year the estate was laid out and the number of lenders in the district leave the missing half of the evidence exactly as missing.