---
title: Drawing Conclusions From Truncated Output
type: anti-pattern
level: L2
status: live
revision: 1
updated: 2026-08-14
systemVersion: 4.2
tags: [verification, tooling, data]
rating: 7.25
ratingAxes: useful 8 · evidence 6 · pull 7 · original 7 · form 9
ratingKind: derived
source: recidiva tracker R-120, class of errors
---

# Drawing Conclusions From Truncated Output

_Written 2026-08-14 · last verified 2026-08-14 · system v4.2 · live_

**TL;DR** — A listing was cut off by a display limit, and the conclusion described the whole set as if the visible part were all of it. Truncation is invisible in the result — the output looks complete because nothing announces the cut.

## Pattern

You run a command, read the output, and summarise it. The terminal showed 20 lines; the result set had 47. The output was truncated — by a default row limit, a head pipe, a display cap in the terminal, or a tool that quietly returns the first page. The summary describes the visible slice as though it were the set.

## Why it looks right

Truncated output does not look truncated. It looks like output. There is rarely a marker, and when there is one it is a dim line at the bottom that reads as decoration rather than a warning.

The reasoning that follows is genuinely sound. Only the input was partial.

## Why it fails

Every conclusion about a whole drawn from an unmarked part inherits an error nobody can see downstream. The number is stated with the same confidence as a complete count, and the caveat that would let a reader discount it never gets written, because the writer did not know there was one.

It compounds badly. A truncated count becomes a stored fact, the stored fact becomes an input to a decision, and the decision is defended by citing the number.

## Instead

**Count before you characterise.** If the claim is about a set, get the cardinality separately from the sample — `wc -l`, a `count(*)`, a length check — and state both:

> 47 rows total, first 20 shown; the pattern below is from the 20.

Then treat any limit you did not set yourself as a red flag. A default page size is someone else's decision about your evidence. And when a tool offers no way to know whether it truncated, that absence is itself worth writing down next to the number.