In an observation method, measurement values of an object of measurement at a plurality of different positions in a plane that intersects a depth direction are acquired from an optical coherence tomography instrument (S100). In the observation method, the measurement values at a same depth position at each of the plurality of positions are averaged (S104). In the observation method, the average values at each of the depth positions are integrated in the depth direction (S105). In the observation method, a shrinkage parameter of the object of measurement is calculated on the basis of the integrated value (S106).