I have been researching about ETFs, and have been looking a bit into different ones for the MSCI world index. I realized that there sometimes is a substantial difference in the development of the ETF and the base index, for example, the ETF
ISHARES CORE MSCI WORLD UCITS ETF - USD ACC (which has ISIN
IE00B4L5Y983), has lost 1.5% in value since March 31, whereas the baseline index, MSCI world, has gained 3% in the same time frame.
Where do these differences come from, and are they normal?