Final answer:
Heritability on the scale of liability refers to the genetic variation that contributes to a trait or disease, while heritability on the scale of observation refers to the actual presence of the trait or disease in an individual.
Step-by-step explanation:
Heritability is the fraction of phenotype variation that can be attributed to genetic differences among individuals. The scale of liability refers to the underlying genetic liability that contributes to the expression of a trait or disease, whereas the scale of observation refers to the observed phenotype or trait itself. For example, in the case of a genetic disorder like cystic fibrosis, the scale of liability would refer to the genetic variation that increases the risk of developing the disease, while the scale of observation would refer to the actual presence of the disease in an individual.