Under the Markowitz model, the risk of a portfolio is measured by the portfolio variance.

True.

Here's why:

1. The Markowitz model, also known as Modern Portfolio Theory, was developed by Harry Markowitz in 1952. This model is used to construct a portfolio of assets in such a way that maximizes expected return for a given level of risk.

2. In the Markowitz model, risk is quantified as the standard deviation of the portfolio's returns. The standard deviation is a measure of how much the returns can vary from the average return. The square of the standard deviation is called variance.

3. Therefore, under the Markowitz model, the risk of a portfolio is indeed measured by the portfolio variance. The model aims to find the portfolio with the minimum variance (and hence the minimum risk) for a given expected return, or the maximum expected return for a given level of variance.

4. It's important to note that the Markowitz model assumes that investors are risk-averse, meaning they prefer less risk to more risk for the same level of expected return. This is why the model focuses on minimizing variance.