Diversification
Diversification combines exposures with imperfectly correlated return drivers in an effort to reduce concentration in specific risks. It can reduce some portfolio variability or loss scenarios, but it does not eliminate systematic risk, guarantee a lower loss, or preserve expected return in every period.
Frequently Asked Questions
How does diversification affect portfolio variance?
Portfolio variance depends on weights, individual variances, and pairwise covariances. Lower or negative covariance can reduce modeled variance, but correlations are estimated from data and can change materially across market regimes.
How many holdings are enough?
There is no universal number. Effective diversification depends on concentration, economic exposures, liquidity, factor loadings, geography, currency, and correlation—not ticker count alone. A small number of broad funds can be more diversified than many overlapping securities, but fund structure and holdings still require review.
Does diversification protect against market crashes?
Not reliably. Assets that appeared weakly correlated can decline together during stress, and liquidity can deteriorate at the same time. Diversification may reduce some sources of risk, but it does not guarantee protection from market-wide or tail events.
Can a portfolio be over-diversified?
Additional holdings can add complexity, fees, taxes, monitoring burden, or unintended overlap without materially changing risk exposures. The relevant question is whether each exposure changes the portfolio's risk drivers after costs and constraints.
How often should a diversified portfolio be rebalanced?
There is no universally optimal schedule. Calendar, threshold, cash-flow, tax, transaction-cost, and risk-budget approaches can produce different outcomes. Rebalancing rules should be documented and tested under the investor's constraints.