F1 2012 VET vs. ALO in Practice and Qualifying

A couple of quick sketches to summarise how Vettel and Alonso have compared over the season to date in practice and qualifying.

First up, the time delta between their best times in each session:

This doesn't take into account the lap length, though, so we can normalise by dividing through by the fastest laptime recorded across VET and ALO for each session:

Casting a quick eye over the charts, I think we could make at least an anecdotal claim that progression continues in qualifying at least... so if VET improves over ALO going Q1 to Q2, then we'll see a further increase going into Q3?

How do P3/third practice times compare with qualifying session times?

VET seems to straddle his P3 time with the Q1 and Q2 times? (Below the line shows the qualifying session time beat the third practice time.)

How about ALO?

Is there a tendency there for ALO to perform better in qualifying than in P3? This is where "proper" statistics come in, not just graphical stats "by eye"... 

So, what statistical test should we use to see how qualifying session times compare with practice times?