Problem with statistics

We have a problem with statistics on 2 tables. We run update statistics on a regular basis. (once every morning and once in the evening). We have a select on the 2 tables and in sqexplain.out we see that this select the optimiser uses a sequential scan instead of using the index. We do an update statistics on this 2 tables and the optimiser takes an index path. How is this possible ? We have 2 ours between the first update statistics and the time that the optimiser takes the wrong path. Doris Willaert doris.willaert@suzuki.be