A computer based system and method of determining whether to re-fetch a previously retrieved document across a computer network is disclosed. The method utilizes a statistical model to determine whether the previously retrieved document likely changed since last accessed. The statistical model is continuously improving its accuracy by training internal probability distributions to reflect the actual experience with change rate patterns of the documents accessed. The decision of whether to access the document is based on the probability of change compared against a desired synchronization level, random selections, maximum limits on the amount of time since the document was last accessed, and other criterion. Once the decision to access is made, the document is checked for changes and this information is used to train the statistical model.