Where does break collide?

In econometrics, a structural break is a point in time at which the parameters of a model, the relationships among its variables, change, so that a single fitted equation no longer holds across the whole sample. Chow's 1960 Tests of equality between sets of coefficients in two linear regressions gave the classic test for a break at a known date, and Bai and Perron's 1998 Estimating and testing linear models with multiple structural changes extended detection to multiple unknown break dates. The referent is a shift in a data-generating process, not an opening pool stroke or a broken symmetry in physics.[1][2]

Unit

The date(s) and magnitude of change in a model's parameters

Recovery means

Not applicable

Measured by

Detected with break tests such as the Chow test and the Bai–Perron procedure, which compare model fit across candidate break points

In physics, symmetry breaking is a situation where the laws governing a system are symmetric but its actual state is not, as when a system settles into one of several equivalent lowest-energy configurations and thereby breaks the symmetry. Nambu and Jona-Lasinio's 1961 model applied spontaneous symmetry breaking to elementary particles by analogy with superconductivity, and Anderson's 1972 More is different argued that broken symmetry is central to how collective order emerges at scale. The referent is a loss of symmetry in a physical state, unrelated to a billiards break or an econometric parameter shift.[3][4]

Unit

The order parameter distinguishing the asymmetric state from the symmetric one

Recovery means

Not applicable

Measured by

Characterised by an order parameter and, often, the massless modes or phase transition that accompany the broken symmetry