This chart shows how badly Strategy's stock has performed since bitcoin's peak
By Tomi KilgoreStrategy stepped up bitcoin buying in the latest week as prices slumped, with the most purchased in four monthsWhile Strategy's stock has fallen a lot more than bitcoin, since bitcoin peaked in early October, the correlation between the two has actually increased.While it's no secret that bitcoin has been falling fast, investors in Strategy may be surprised at how much farther the cryptocurrency stockpiler's shares have dropped in recent weeks and months.Bitcoin's (BTCUSD) fall below $100,000 last week - the first time in months, while also entering a bear market - hasn't reduced Strategy's (MSTR) appetite for the digital currency. The company just made its largest purchase of bitcoin over a week's time in more than three months.On Monday, the stock has dropped 2.2%, while bitcoin shed another 0.5%, below the $92,000 level.Although Strategy is technically classified as a software company, the stock has traded more like bitcoin than its software peers ever since the company adopted the cryptocurrency as its primary treasury reserve asset in 2020.In recent weeks, investors using Strategy stock as a proxy for bitcoin may have become increasingly worried that the stock and bitcoin may have decoupled as bitcoin sold off, with Strategy's stock getting punished a lot more. Since bitcoin peaked on Oct. 6, it has tumbled about 26% to a six-month low, according to FactSet data, while Strategy shares have plunged about 48% toward a 13-month low.What could be more troubling for investors is that if anything, the stock and bitcoin are now more in sync - at least in terms of daily direction - than they were earlier this year. Basically, Strategy's stock is doing what investors want it to do - be highly correlated with bitcoin - it's just getting hurt a lot more on the way down.Sometimes, that's how proxies work; the direction might be similar, but the gains and losses may get exaggerated.From the start of the year through July 16, when Strategy shares closed at an eight-month high, the stock had gained 57.4% while bitcoin had rallied 27.3%. The correlation coefficient between the stock and bitcoin during that time was 0.80. A reading of 1.00 would mean they always moved in the same direction.But since then, the correlation has been 0.82, even as the stock has lost 58% and bitcoin has fallen 22%. And since bitcoin's peak on Oct. 6, the correlation has actually increased to 0.94, even though Strategy's stock has sold off a lot more.This comes as Strategy disclosed Monday that it spent $835.6 million to acquire 8,178 bitcoin over the week from Nov. 10 through Nov. 16. The average purchase price per bitcoin was $102,171, or 9.5% above current levels.That was nearly five times what the company had purchased over the previous five weeks - it had bought 1,662 bitcoin during that time - and the most since the company bought 21,021 bitcoin during the week through Aug. 3, at an average price of $117,256 per bitcoin.The company said it owned 649,870 bitcoins as of Nov. 16. It has spent $48.37 billion to buy its stock of bitcoin, and has paid an average price of $74,433 per bitcoin. At current prices, the value of its holdings would be $60.09 billion.Strategy shares have shed 43.8% over the past 12 months, while bitcoin has gained 1.7%, the State Street SPDR S&P Software & Services ETF XSW has ticked up 0.3% and the S&P 500 index SPX has advanced 14.1%.-Tomi KilgoreThis content was created by MarketWatch, which is operated by Dow Jones & Co. MarketWatch is published independently from Dow Jones Newswires and The Wall Street Journal.