the present study predicted that each dark trait would positively correlate with the loud car scale aggregate, and because typically modifications to vehicles represent criminal activity, it was predicted that sadism and psychopathy would positively predict the aggregate of the car items.

To me it seems like they’re saying “predicted” when they meant “hypothesized”.

Here are the questions they used:

The items were: “My car is an extension of what makes me a person”, “I think loud cars are really cool”, and “If I could, I would make my car louder with muffler modification”. Items were responded to using the following response key: 1 – strongly disagree, 2 – somewhat disagree, 3 – neither agree nor disagree, 4 – somewhat agree, or 5 – strongly agree.

I think what’s missing from the survey design are questions which explore intent, like “I would use a loud muffler when people are sleeping”. I also think the “makes me a person” and “really cool” wording is ambiguous because the answers are not necessarily related to one’s personality. For example “makes me a person” could refer to maybe “helps me achieve survival” to someone, and “really cool” could mean anything from deep interest hobby to expressing admiration of other people’s abilities.

The other issue is that their sample is only business students, so it’s not representative of the entire male population.

I think maybe they released this pilot to gather initial impressions, so it makes sense to be critical and make suggestions for improvements

Edit I think another issue is that people in general don’t understand the disposition of the loud muffler enthusiast, and the approach in this study is starting out with the assumption that the motivation is dark tetrad.