I've reimplemented the statistics module from the science collection to use sequences instead of just vectors. I like the generality better - I can use any sequence (e.g., vector or list) - but there is more of performance hit than I would have liked. I haven't timed it with the new changes that Matthew just put it. The good news is that there isn't much of a hit for using (variance data) as opposed to (variance (in-vector data)) and there isn't a huge hit for using the contract that ensures that the sequence is a sequence of real numbers. I created a 100000 element vector and timed a loop getting the variance of the elements 10 times. Note that I create an executable that runs compiled code in both cases. [Runs of the sequence code within DrScheme are about twice the times of the compiled code - I assume they run from byte code in that case. Runs of the science collection code is about the same in DrScheme - I assume they run the compiled code.] Times using sequences [primarily using 'for/fold' for sequencing and referencing]: (variance data) : cpu time: 625 real time: 625 gc time: 32 (unchecked-variance data) : cpu time: 531 real time: 531 gc time: 77 (variance (in-vector data)) : cpu time: 609 real time: 609 gc time: 16 (unchecked-variance (in-vector data)) : cpu time: 485 real time: 484 gc time: 0 Times using vectors (current science collection routines) [primarily using 'do' for sequencing with 'vector-ref' for referencing]: (variance data) : cpu time: 235 real time: 234 gc time: 16 (unchecked-variance data) : cpu time: 187 real time: 188 gc time: 46 All of the normal caveats about timing values apply - just because I'm timing a statistics routine doesn't been it's statistically relevant :). I will retime them when there is a nightly build with Matthew's performance improvements is available (it seems that 4.2.1.7 from Saturday is the latest) - or I build it on my machine at home. I don't have the development tools on my laptop to build from svn. I've attached the files in case anyone wants to look them over. If someone could run them against the latest svn, it would be nice. [ Comments from anyone that uses these routines from the science collection would be most welcome. Doug