Overlapping area represents the amount of risk that can be diversified away by holding PowerShares QQQ ETF and iShares Russell 1000 Growth ET in the same portfolio assuming nothing else is changed. The correlation between historical prices or returns on iShares Russell 1000 and PowerShares QQQ is a relative statistical measure of the degree to which these equity instruments tend to move together. The correlation coefficient measures the extent to which returns on PowerShares QQQ ETF are associated (or correlated) with iShares Russell. Values of the correlation coefficient range from -1 to +1, where. The correlation of zero (0) is possible when the price movement of iShares Russell 1000 has no effect on the direction of PowerShares QQQ i.e. PowerShares QQQ and iShares Russell go up and down completely randomly.