 Direct measurement. Radical behavior analysis is all about direct measurement. It's as I cannot overestimate or overstate the importance of direct measurement. When you're talking about direct measurement, you're talking about measure the thing that you're interested in directly. So we're not going to measure something else to indicate that another behavior has happened. The behavior of interest, we're going to measure directly. If you look into my history a wee bit, you'll understand that I did a lot of work with risky behavior, which often includes sexual behavior. We had a challenging time in our lab because we wanted to measure things directly. How often do people use condoms? As you might imagine, the IRB was not okay with us going to people's rooms. We watched them have sex to find out if they actually used the condom. But behavior analytically, it would have been a much better experiment if we did or a much better study if we did. But we couldn't. We had to use indicators of that. Indicators or indirect measurements about people saying how often they did. Indirect. We need to directly observe how often those condoms were used if we wanted to make sure that we had a good, solid sound science behind our study.