Lack of activity. People who are less active spend more time in front of a computer, and people who are less active have higher, have higher blood pressure. And if you were to control for this, if you were to take a bunch of people who had a similar lack of activity, or had a similar level of activity, you might see that computer time does not correlate with blood pressure. That these are just both driven by the same thing. And what you're really seeing here is like, okay, people with high lack of activity who aren't active, well it drives both of these variables. So once again, when you do this observational study, and if you do it well, you can draw correlations, and that might give you decent hypotheses for causality, but this does not show causality. Because you could have these confounding variables.