William RulonMiller - CSS Industries Insider

The ability to find closely correlated positions to Microsoft could be a great tool in your tax-loss harvesting strategies, allowing investors a quick way to find a similar-enough asset to replace Microsoft when you sell it. If you don't do this, your portfolio allocation will be skewed against your target asset allocation. So, investors can't just sell and buy back Microsoft - that would be a violation of the tax code under the "wash sale" rule, and this is why you need to find a similar enough asset and use the proceeds from selling Microsoft to buy it.

The correlation of Microsoft is a statistical measure of how it moves in relation to other instruments. This measure is expressed in what is known as the correlation coefficient, which ranges between -1 and +1. A perfect positive correlation (i.e., a correlation coefficient of +1) implies that as Microsoft moves, either up or down, the other security will move in the same direction. Alternatively, perfect negative correlation means that if Microsoft moves in either direction, the perfectly negatively correlated security will move in the opposite direction. If the correlation is 0, the equities are not correlated; they are entirely random. A correlation greater than 0.8 is generally described as strong, whereas a correlation less than 0.5 is generally considered weak.