As the retirement research has evolved over the decades, so too have the “optimal” retirement strategies, and the entire approach to the retirement planning process itself.
In the early years, optimal retirement planning was all about determining which portfolio on the efficient frontier was best suited to achieve retirement goals. Then advisors shifted to a more goals-centric approach, where clients pursued a Maslow-style hierarchy of goals, from the “basic” essential goals of retirement (e.g., food, clothing, and shelter), to the more discretionary wants and wishes. And in recent years, retirement planning has increasingly shifted towards a more holistic “household balance sheet” approach that aims to capture all of the household’s present and future assets and liabilities, to determine if the household is fully funded (or if not, what its funded ratio is).
And in a recent paper, researchers Patrick Collins and Francois Gadenne note that each of these retirement modeling approaches has their own “shape” – from the curve of the efficient frontier, to the triangle of the Maslow-style hierarchy of retirement needs, to the rectangle of the household balance sheet with its assets and liabilities. And each shape leads to its own unique views on what is “best” for retirement planning, and what is considered “safe” – from cash under the curve approach (the most conservative portfolio on the efficient frontier), to the lifetime annuity under the triangle approach (guaranteeing that essential expenses are covered for life), to a laddered portfolio of TIPS bonds with the rectangle approach (aiming to perfectly match assets to liabilities and immunize the household against future changes in interest rates or inflation).
Yet ultimately, while each of the different shapes of retirement planning may prescribe different recommendations, it’s still not entirely clear which is “best”. After all, the rectangle approach may be effective to determine the household’s funded ratio and explore what’s possible, but is a poor framework for making trade-off decisions about which goals to prioritize. And while the triangle approach is better for prioritizing goals, it doesn’t necessarily produce a clear portfolio allocation the way the efficient frontier curve does.
Which means in the end, the best approach for retirement planning may incorporate all three – the rectangle to explore the Possibilities, the triangle to Prioritize, and the curve to allocate the Portfolio itself!