Diversification & the Rule of 100
Overview
You’ve learned several concepts throughout the Achievable material about making suitable investor recommendations. Here, we’ll focus on the strategies, styles, and techniques used to build suitable investor portfolios.
🔑 This chapter focuses on these investment considerations:
- Diversification
- Rule of 100
- ESG considerations
- Religious-based considerations
Diversification
Many financial professionals cite diversification as one of the most important investing principles. Markets change quickly, and even well-known industries can be hit by unexpected events.
Illustrations used by the text:
| Example | What happened |
|---|---|
| 2020 industry shifts | Resurgence in drive-in theatres; major downturn in the airline industry |
| American Airlines (AAL) | Traded around $30 per share in November 2019 and fell to about $11 per share in November 2020. A $100,000 portfolio fully invested in AAL in November 2019 would have had less than $37,000 one year later |
| Collapsed concentrated positions | Enron, Bear Stearns, and Silicon Valley Bank |
| George Maddox (Enron plant manager) | Lost over $1 million in retirement accounts due to Enron’s bankruptcy. He allegedly held almost all of his retirement savings (roughly $1.3 million) in Enron stock. Concentration helped during the stock’s dramatic rise in the late 1990s, but his savings collapsed after revelations of fraudulent accounting practices made the stock worthless |
A lack of diversification is a major red flag in a portfolio. Even if a concentrated investment has performed well, putting significant sums into one or a few investments is rarely a good idea.
Exceptions — products diversified “inside”
| Product | Why it is internally diversified |
|---|---|
| Life cycle fund | Typically holds many mutual funds, and each mutual fund may hold dozens or hundreds of securities |
| Index funds and exchange traded funds (ETFs) tracking broad indexes (like the S&P 500) | Can provide high levels of diversification through a single investment |
Employment-related concentration
A common diversification issue comes from employment-related benefits. Employees of publicly traded companies may receive company stock at a discount or as a benefit. It’s easy to feel comfortable investing heavily in the company you work for because you feel you have an “insider’s view” of the business. Still, there are no guarantees (see the George Maddox story).
Financial representatives should identify when a client is overly concentrated and recommend adding variety.
Rule of 100
An investor’s age is an important suitability factor. In general, age and risk tolerance tend to move together:
| Investor | Suitability tendency |
|---|---|
| Younger investors | More likely to be suitable for aggressive strategies with higher risk |
| Older investors | More likely to be suitable for conservative strategies with lower risk |
🔑 We previously discussed the rule of 100 in the common stock unit. It’s a general guideline for asset allocation:
100 − investor’s age = % of the portfolio allocated to stocks
The remainder is allocated to bonds.
| Age | Stock % | Bond % |
|---|---|---|
| 30 | 70% | 30% |
| 45 | 55% | 45% |
| 60 | 40% | 60% |
| 70 | 30% | 70% |
⚠️ The rule of 100 is not absolute. It’s a starting point for the “average” investor at a given age, and it may not fit investors with unusual circumstances. For example:
| Unusual circumstance | Possible suitable allocation |
|---|---|
| An 80-year-old multi-millionaire who wants an aggressive approach with a small portion of their net worth | Could be suitable for a 100% stock portfolio |
| A 25-year-old unemployed investor with large debt levels | Might have no stock exposure |
When using the rule of 100, you still need to consider the client’s full financial picture and adjust recommendations when appropriate.
ESG considerations
Historically, many investors chose securities primarily based on risk and return. Today, many investors also consider whether an investment aligns with their personal values, even if that reduces the number of suitable choices. Environmental, social, and governance (ESG) considerations are a common form of what some analysts call “ethical investing.”
Definitions
| Term | Definition | Example |
|---|---|---|
| Ethical investing | Choosing investments based on moral-based factors, including political, religious, or social values | ESG-based investing; religious-based investing |
MSCI ESG score
A common industry standard for evaluating ESG factors is the Morgan Stanley Capital International (MSCI) ESG score. MSCI is an investment research firm associated with Morgan Stanley.
MSCI assigns a general ESG score of ‘leader,’ ‘average,’ and ‘laggard’ to the investments it evaluates.
The three pillars
| Pillar | Focus | MSCI factors considered |
|---|---|---|
| Environmental | An investment’s environmental impact | Climate change impact; Natural capital (e.g., water, lumber) usage; Pollution & waste; Environmental opportunities (e.g., using sustainable technology) |
| Social | How an investment relates to people and human rights | Human capital (e.g., health & safety); Product liability (e.g., product safety & quality); Stakeholder opposition (e.g., community relations); Social opportunities (e.g., improving health outcomes of customers) |
| Governance | The business structure of the investment | Corporate governance (e.g., ownership, worker pay); Corporate behavior (e.g., ethics, transparency) |
MSCI evaluates these three pillars and assigns ratings to many widely followed investments.
A high ESG rating does not guarantee strong returns. Example: Plug Power Inc. (ticker: PLUG), a sustainable energy company, is assigned a ‘leader’ rating by MSCI (as of June 2023). However, from January 2021 to June 2023, PLUG stock declined more than 80% in value.
This can create a practical challenge for investment advisers: a client may only accept recommendations if the ESG score is high, even when that narrows the opportunity set. In general, ESG constraints can mean fewer choices and potentially lower returns. Regardless, financial professionals must consider and prioritize client preferences.
Religious considerations
Similar to ESG-based ethical investing, some investors choose securities based on religious or spiritual beliefs. Depending on the investor’s religion, spirituality, or denomination, different screens may be used to identify acceptable investments. For example, some Christian and Islamic investors avoid securities tied to addictive industries (e.g., tobacco, gambling).
It can be difficult for an investor to identify individual securities that comply with specific religious beliefs. However, several mutual funds maintain objectives tied to specific religions.
| Fund | Ticker | Religious basis |
|---|---|---|
| LKCM Aquinas Value Fund | AQEIX | Catholicism-based fund |
| Amana Income Fund | AMANX | Islamic-based fund |
| New Covenant Growth Fund | NCGFX | Presbyterian-based fund |
As with ESG investing, religious-based investing may result in fewer choices and lower rates of return. Again, financial professionals must consider and prioritize their clients’ preferences.
Key points
Diversification
- Allocating capital among multiple asset classes and securities
- Reduces non-systematic risks
Rule of 100
- Determines appropriate asset allocation based only on age
- 100 minus age = % in stocks
ESG considerations
- Choosing investments based on these factors:
- Environmental considerations
- Social considerations
- Governance considerations
- May result in fewer choices and lower returns
- Regardless, advisers must abide by client preferences
Religious considerations
- Choosing investment based on religious or spiritual factors
- May result in fewer choices and lower returns
- Regardless, advisers must abide by client preferences
Sources
Primary/official references for the material in this chapter. Every link was fetched and returned HTTP 200 on 2026-08-15.
| # | Source | Publisher |
|---|---|---|
| 1 | Markowitz/Sharpe — portfolio theory and CAPM, the source work | Nobel Prize |
| 2 | Rule 2111 — suitability, reasonable-basis/customer-specific/quantitative | FINRA |
| 3 | Uniform Prudent Investor Act — portfolio-level fiduciary standard | Uniform Law Commission |
| 4 | Achievable Series 65 — chapter 2.3.1 | Achievable (course text) |