The most recent short interest data has been released for the 01/12/2018 settlement date, which shows a 553,785 share increase in total short interest for Portola Pharmaceuticals, Inc. (PTLA), to 4,455,929, an increase of 14.19% since 12/29/2017. Total short interest is just one way to look at short data; another metric that we here at Dividend Channel find particularly useful is the "days to cover" metric because it considers both the total shares short and the average daily volume of shares traded. The number of shares short is then compared to the average daily volume, in order to calculate the total number of trading days (at the average volume) it would take to close out all of the open short positions if every share traded represented a short position being closed. Average daily volume for PTLA at the 01/12/2018 settlement decreased to 921,603, as compared to 1,377,028 at the 12/29/2017 report. That brought "days to cover" up to 4.83, a 70.62% increase from the 2.83 days to cover calculated at the previous short interest data release.The below chart shows the historical "days to cover" for PTLA at previous short interest release dates: An increased "days to cover" value could indicate that short sellers are using the stock to hedge a long bet elsewhere, or could also mean that short sellers believe the stock will decline in price. When short sellers eventually cover their positions, by definition there must be buying activity because a share that is currently sold short must be purchased to be covered. So investors tend to keep an eye on that "days to cover" metric, because a high value could predict a sharper price increase should the company put out some unexpectedly good news — short sellers might then rush to cover their positions, and if the "days to cover" number is high, it would then be more difficult to close those positions without sending the stock higher (until the higher price produces enough sellers to generate the necessary volume the short sellers need to close their positions). The chart below shows the one year performance of PTLA shares, versus its 200 day moving average. Looking at this chart, PTLA's low point in its 52 week range is $26.90 per share, with $67.10 as the 52 week high point — that compares with a last trade of $47.11. According to the ETF Finder at ETF Channel, PTLA makes up 1.29% of the SPDR S&P Biotech ETF (XBI) which is up by about 0.4% on the day Wednesday.