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If you own shares in BlueScope Steel Limited (ASX:BSL) then it's worth thinking about how it contributes to the volatility of your portfolio, overall. In finance, Beta is a measure of volatility. Volatility is considered to be a measure of risk in modern finance theory. Investors may think of volatility as falling into two main categories. First, we have company specific volatility, which is the price gyrations of an individual stock. Holding at least 8 stocks can reduce this kind of risk across a portfolio. The second sort is caused by the natural volatility of markets, overall. For example, certain macroeconomic events will impact (virtually) all stocks on the market.

Some stocks mimic the volatility of the market quite closely, while others demonstrate muted, exagerrated or uncorrelated price movements. Beta is a widely used metric to measure a stock's exposure to market risk (volatility). Before we go on, it's worth noting that Warren Buffett pointed out in his 2014 letter to shareholders that 'volatility is far from synonymous with risk.' Having said that, beta can still be rather useful. The first thing to understand about beta is that the beta of the overall market is one. A stock with a beta below one is either less volatile than the market, or more volatile but not corellated with the overall market. In comparison a stock with a beta of over one tends to be move in a similar direction to the market in the long term, but with greater changes in price.

See our latest analysis for BlueScope Steel

What does BSL's beta value mean to investors?

Looking at the last five years, BlueScope Steel has a beta of 0.91. The fact that this is well below 1 indicates that its share price movements haven't historically been very sensitive to overall market volatility. This suggests that including it in your portfolio will reduce volatility arising from broader market movements, assuming your portfolio's weighted average beta is higher than 0.91. Many would argue that beta is useful in position sizing, but fundamental metrics such as revenue and earnings are more important overall. You can see BlueScope Steel's revenue and earnings in the image below.

Could BSL's size cause it to be more volatile?

BlueScope Steel is a fairly large company. It has a market capitalisation of AU$6.2b, which means it is probably on the radar of most investors. It is a little unusual to see big companies like this trade on low beta values. Oftentimes there is some other clear influence on the share price, overshadowing market volatility.