Ohio Rev. Code § 4909.151
In fixing the just, reasonable, and compensatory rates, joint rates, tolls, classifications, charges, or rentals to be observed and charged for service by any public utility, the public utilities commission may consider the costs attributable to such service. The utility shall file with the commission an allocation of the cost, except cost related to sparsity of population, for services for which a change in rates is proposed when evidence relating thereto is presented which indicates that the rate or rates do not generally reflect the cost of providing these services. As used in this section, "costs" includes operation and maintenance expense, depreciation expense, tax expense, and return on investment as actually incurred by the utility. The costs allocated to each service shall include only those costs used by the public utilities commission to determine total allowable revenues.
R.C. § 4909.151