By the end of this lesson you understand what criterion guides how much weight a position should have in a portfolio, without it being a universal formula.
\nThe two previous lessons introduced concentration risk and correlation between assets. This lesson closes the module with the question both leave open: how much specific weight should a position have within a portfolio?
\nPosition sizing is the criterion for deciding how much weight a specific position should have, within the asset allocation already decided in Module 1. It's a tool for controlling how much that position contributes to the portfolio's risk -- not a universal formula or a fixed percentage that automatically determines how much anyone should invest in any position.
\nThat criterion rests on the two factors introduced in the previous lessons. The first is the concentration risk the position itself introduces: the greater its weight within the portfolio, the greater the part of the total exposed to whatever happens specifically to that position. The second is its correlation with the rest of the portfolio: a position highly correlated with the others contributes more to overall risk than a low-correlation position, even with the same nominal weight -- because what affects one tends to also affect those correlated with it, while a poorly correlated position cushions part of that effect.
\nThere's no single formula or universal percentage valid for any investor or any position. What does exist is a criterion: the greater the concentration risk a position introduces, or the more correlated it is with the rest of the portfolio, the smaller its relative weight should generally be -- and conversely, a position with lower concentration risk and lower correlation with the rest can generally sustain a larger relative weight without raising the overall risk as much.
\nThis completes the module: concentration risk, correlation between assets, and the position-sizing criterion together give you the tools to manage risk within an already diversified portfolio.
\nTwo positions of the same nominal weight within a portfolio don't contribute equally to its risk if one is highly correlated with the rest of the portfolio and the other isn't: the first amplifies whatever is already happening to the whole when it's affected, while the second cushions part of that effect by not moving the same way.
\nPosition sizing is the criterion for deciding how much weight a position should have, resting on the concentration risk it introduces and its correlation with the rest of the portfolio -- a tool for controlling its contribution to risk, not a universal formula or a fixed percentage valid for every case.
\nWhy are concentration risk and correlation the two factors that guide how much weight a position should have?
\nWhy isn't there a universal percentage valid for sizing any position in any portfolio?
","sortOrder":3,"readingMinutes":7,"difficulty":"Intermedio"},"previous":{"id":75,"moduleId":27,"slug":"what-is-correlation-between-assets","title":"What is correlation between assets?","summary":"You understand what correlation between assets is and why it's the real mechanism through which diversifying reduces risk.","bodyMarkdown":"## Objectives\n\nBy the end of this lesson you understand what correlation between assets is and why it's the real mechanism through which diversifying reduces risk.\n\n## Content\n\nThe previous lesson introduced concentration risk -- the problem diversifying solves. This lesson names the mechanism that makes diversifying work: correlation between assets, something Module 2 described only in qualitative terms, without naming it.\n\nCorrelation measures the tendency of two assets to move in the same direction, in opposite directions, or independently, in response to the same events. Two highly correlated assets tend to rise and fall together: what affects one tends to affect the other similarly. Two assets with low, or even negative, correlation don't move similarly -- they can react differently, or even in opposite directions, to the same event.\n\nThis is precisely what makes diversifying work: combining assets with low correlation to each other reduces the portfolio's overall risk more than combining highly correlated assets would, even if both combinations spread the same capital across the same number of positions. Two companies in the same sector tend to have higher correlation with each other than two companies in unrelated sectors, because they share more factors that affect them similarly -- the same idea as sector diversification, already covered in Module 2, now explained from its underlying mechanism.\n\nIt's important not to confuse correlation with volatility, already covered in Level 1: volatility measures how much a single asset moves on its own, while correlation measures how two assets move relative to each other. They're distinct properties -- an asset can be very volatile and, at the same time, have low correlation with another asset in the portfolio, and a low-volatility asset can still be highly correlated with another.\n\n## Example\n\nTwo companies in the same tech sector tend to rise and fall together in response to news affecting that sector -- they have high correlation. A tech company and a company in an unrelated sector -- food, for example -- don't usually react the same way to that same news: their correlation is lower, and combining them reduces the portfolio's overall risk more than combining two similar tech companies would.\n\n## Common mistakes\n\n- Thinking combining many assets is enough for good diversification, without considering whether they're correlated with each other.\n- Confusing correlation with volatility -- a low-volatility asset can still be highly correlated with another, and a highly volatile asset can have low correlation with the rest of the portfolio.\n\n## Summary\n\nCorrelation measures how two assets move relative to each other in response to the same events -- the real mechanism through which combining low-correlation assets reduces a portfolio's risk more than combining highly correlated ones. It shouldn't be confused with volatility, which measures how much a single asset moves on its own.\n\n## Self-check\n\nWhy does combining low-correlation assets reduce a portfolio's risk more than combining highly correlated assets?\n\nWhy are correlation and volatility distinct properties of an asset?","bodyHtml":"By the end of this lesson you understand what correlation between assets is and why it's the real mechanism through which diversifying reduces risk.
\nThe previous lesson introduced concentration risk -- the problem diversifying solves. This lesson names the mechanism that makes diversifying work: correlation between assets, something Module 2 described only in qualitative terms, without naming it.
\nCorrelation measures the tendency of two assets to move in the same direction, in opposite directions, or independently, in response to the same events. Two highly correlated assets tend to rise and fall together: what affects one tends to affect the other similarly. Two assets with low, or even negative, correlation don't move similarly -- they can react differently, or even in opposite directions, to the same event.
\nThis is precisely what makes diversifying work: combining assets with low correlation to each other reduces the portfolio's overall risk more than combining highly correlated assets would, even if both combinations spread the same capital across the same number of positions. Two companies in the same sector tend to have higher correlation with each other than two companies in unrelated sectors, because they share more factors that affect them similarly -- the same idea as sector diversification, already covered in Module 2, now explained from its underlying mechanism.
\nIt's important not to confuse correlation with volatility, already covered in Level 1: volatility measures how much a single asset moves on its own, while correlation measures how two assets move relative to each other. They're distinct properties -- an asset can be very volatile and, at the same time, have low correlation with another asset in the portfolio, and a low-volatility asset can still be highly correlated with another.
\nTwo companies in the same tech sector tend to rise and fall together in response to news affecting that sector -- they have high correlation. A tech company and a company in an unrelated sector -- food, for example -- don't usually react the same way to that same news: their correlation is lower, and combining them reduces the portfolio's overall risk more than combining two similar tech companies would.
\nCorrelation measures how two assets move relative to each other in response to the same events -- the real mechanism through which combining low-correlation assets reduces a portfolio's risk more than combining highly correlated ones. It shouldn't be confused with volatility, which measures how much a single asset moves on its own.
\nWhy does combining low-correlation assets reduce a portfolio's risk more than combining highly correlated assets?
\nWhy are correlation and volatility distinct properties of an asset?
","sortOrder":2,"readingMinutes":7,"difficulty":"Intermedio"},"next":null,"pathContext":null,"curatedLinks":{"prerequisite":[],"continuation":[],"related":[]},"relatedConcepts":[{"concept":{"id":84,"slug":"position-sizing","term":"Position sizing","shortDefinition":"The criterion for deciding how much weight a position should have in a portfolio based on how much concentration risk it introduces and how correlated it is with the rest -- a tool for controlling its contribution to risk, not a universal formula.","longDefinition":"Position sizing is the criterion for deciding how much weight a specific position should have within a portfolio, inside the asset allocation already decided in Module 1. It rests on two factors: the concentration risk a position introduces -- the greater its weight, the greater the part of the portfolio exposed to whatever happens specifically to that position -- and its correlation with the rest of the portfolio -- a position highly correlated with the others contributes more to overall risk than one with low correlation, even with the same nominal weight. It's a tool for controlling how much a specific position contributes to a portfolio's risk, not a universal formula or a fixed percentage that automatically determines how much anyone should invest in any position."}}]}