The State Equal Retirement Benefit Fund is created. The fund shall be administered by the board. Each state agency participating in the retirement system shall make a contribution at least once a year to the fund, in addition to any other retirement contributions. Such contribution shall be in an amount determined by the board to provide all similarly situated male and female members of the retirement system with equal benefits pursuant to subsection (2) of section 84-1319 and to provide for direct expenses incurred in administering the fund. The amount contributed to the fund by each state agency participating in the retirement system shall be proportionate to the total amount such agency contributes to the system for retirement benefits. Any money in the fund available for investment shall be invested by the state investment officer pursuant to the Nebraska Capital Expansion Act and the Nebraska State Funds Investment Act.