GDX and GDXJ vs. GLD

How are behaviors of physically backed gold and gold miner exchange-traded funds (ETF) similar and different? To investigate we consider each of Market Vectors Gold Miners (GDX) and VanEck Vectors Junior Gold Miners ETF (GDXJ) versus SPDR Gold Shares (GLD). Using daily returns for GDX since May 2006 and GDXJ since November 2009, and contemporaneous daily returns for GLD and the S&P 500 Index (SP500), all through early September 2020, we find that: