here to tell us more about all this is susan dentzer. she's the editor-in-chief of "health affairs," and a health analyst for the newshour. welcome back, as always. >> great to be back, margaret. >> warner: pretty stunning finding. one third of all people who check into the hospital develop something in the hospital? >> very shocking indeed. our study looked at a new way of going back over hospital records and looking for signs of something bad had happened and investigating those and making sure that something untoward had happened. in fact, when that was done for one month in 2004 at three hospitals that were very sophisticated hospitals in the united states that had very advanced patient safety programs still one in three of the hospital admissions during that month had an adverse event associated with them. we don't know how much harm or injury or death. but, for example, it's things like if you have what's called a central line which is a tube that can be inserted in your chest, if you're very seriously ill, to deliver medication or