Missing Data Is Not Zero: A Safety Study Worksheet

Define the status before entering a number

A fictional team expects one observation report from each of four review visits. Visit A records three observations. B confirms none. C has no report. D records two. The exercise asks for the information currently available, not a guess about what happened during Visit C.

Use zero only for the confirmed zero in B. Mark C missing. If a visit did not take place, that would need a separate status as well. “No report, ” “no visit, ” and “a completed visit with no observations” describe different events, even if an unlabelled spreadsheet makes them look alike.

Keep a number column and a status column

The known total is five observations from three available reports. The total across all four visits is not established. Dividing five by four would silently treat the missing report as a zero, an assumption the case does not support.

Separate reported-group arithmetic from a complete result

If the task specifically requests the average among available reports, calculate 5 / 3, approximately 1.67 observations per available report. Label that denominator. It is not a complete four-visit average and need not represent the missing visit.

When C later arrives with four observations, the four-visit total becomes nine and the average becomes 9 / 4, or 2.25. The earlier reported-group calculation was not necessarily an arithmetic error; it described an incomplete set. Preserve the earlier coverage statement so readers understand why the result changed. A different data-availability date can change a report without changing historical events.

Write an honest incomplete-data note

A useful note is: “Three of four expected visit reports are available. They record five observations; the fourth report is outstanding.” This tells the reader both the known result and the reporting gap. It does not speculate that the missing report will improve or worsen the result.

Before using blanks in a practice calculation, find the dataset’s definitions for missing, zero, not applicable and pending. Do not borrow meanings from another spreadsheet. When creating your own worksheet, use a clear status field, keep totals reproducible, and avoid formatting that turns absent data into a success signal.