The phrase "considerable variability" means that there is a large amount of difference or variation among different things or situations. Full definition
As you click forward in the interactive, note that each data set shows considerable variability in yearly measurements but when this variability is averaged over time, definite trends can be observed. (serc.carleton.edu)
There is considerable variability among the 14 state documents in the complexity of the reading / language arts standards by grade level. (ciera.org)
Recent evidence indicates that dogs maintained in households require fewer calories per day than dogs kept in kennels, but considerable variability exists. (merckvetmanual.com)