There's significant variability. There are many factors that determine the distribution of ozone over the Arctic: the chemical reactions, the solar exposure, polar stratospheric clouds, the snow and ice distribution. These parameters change from year to year. It is a challenge to try to weave the story together, to tease out what is contributing to what.
Environment Canada scientists are working hard on that. This involves a combination of not just working with the data, but working with the numerical models, the satellite observations, as I had mentioned earlier.
This is not a question of collecting the data, noting that the hole is changing in size; we want to go one step further and try to ask the question of why this is happening. That's the much bigger story that I already mentioned.