Glossary
Definitions of 10 statistical, methodological, and governance terms that recur across our evaluations. Authored and signed off by the editorial team.
Statistics
Bland-Altman Plot
A chart for judging whether two measurement methods agree: each pair's difference is plotted against the pair's average, with limits of agreement.
MAD
An abbreviation with several meanings; in this publication, the median absolute deviation of an app's per-meal errors, a robust measure of their spread.
MAE
Mean absolute error: the average size of an app's per-meal miss, in kilocalories, ignoring whether it was over or under.
MAPE
Mean absolute percentage error: the average per-meal miss as a share of the meal's true calories; the headline accuracy metric in Methodology v3.2.
Governance
Methodology
Evidence Grade
A rating of how much confidence a body of evidence deserves, from high to very low, based on design, bias, consistency, directness and precision.
Ground Truth
The best available value for what was actually measured, used as the yardstick an instrument's readings are checked against.
Replicability
Whether a finding holds up when a different team repeats the study with new data and a comparable method.
Validation Study
A study that checks a measuring tool's readings against a trusted reference to find out how close, and how consistent, the tool is.
Weighed Portion Reference
A test meal whose calories are known because every ingredient was weighed and converted with composition data before the meal was logged.