The demands they are a-changin'

Smooth operators such as time trends are often applied to deal with unidentified demand shifters. However, if unknown factors affect demand irregularly, a time trend fails to capture the variation. We present an index approach for estimating irregular demand shifts, decomposing total demand shifts into predicted and unexplained effects. This allows separating demand shifts caused by known factors like income and substitution effects from unknown impacts on demand. Our application on farmed salmon shows unknown factors impact demand irregularly both between regions and within regions over time. Unknowns contribute to more than half of global salmon demand growth in recent years.