Graphical Integrity

Overview

A graphic has integrity when the physical size of the marks on its surface is directly proportional to the numbers they stand for. Most distortions are not random: they systematically exaggerate the magnitude of recent change. Tufte's contribution is to make distortion measurable — the Lie Factor turns "this chart feels misleading" into a number you can compute and defend.

Sourcing note. Tufte computes and publishes five Lie Factors in VDQI Ch. 2: fuel economy 14.8 (p. 57); the Time "In the Barrel" oil-price barrel 9.4 — +454% drawn as +4,280% (p. 62); the Washington Post oil derricks 9.5 — 708% drawn as 6,700% (p. 62); the shrinking family doctor 2.8 (p. 69); and 59.4 — "a record" — when the Time barrel is read as a volume, 27,000% vs. 454% (p. 71). Any other numeric figure in this skill is an illustrative derivation of the stated mechanism, labeled as such — never cite it as a Tufte-stated value.

§1. The Lie Factor

The single measurement that converts opinion into evidence:

Lie Factor = (size of the effect shown in the graphic) / (size of the effect in the data)

"Size of effect" is a percentage change: (later − earlier) / earlier × 100. Compute it once for the data, once for the printed marks (line lengths, bar heights, icon areas), then divide.

Thresholds: