Two authors published a study in $1992$ of the effect of minimum wages on teenage employment using a U$.$S$.$ state panel. The paper used annual observations for the years $1977-1989$ and included all $50$ states plus the District of Columbia. The estimated equation is of the following type

$(E_{it})={}_0+{}_1(\frac{M_{it}}{W_{it}})+{}_{2}D{2}_i+$dots$+{}_{n}D{51}_i+{}_{2}B{2}_t+$dots$+{}_{T}B{13}_t+u_{it}$

where $E$ is the employment to population ratio of teenagers, $M$ is the nominal minimum wage, and $W$ is average wage in the state. In addition, other explanatory variables, such as the prime$-$age male unemployment rate, and the teenage population share were included.