Throwing in my $0.02, a correlation study is technically an option, where you look at differences as microplastics increase in concentration. But. my instinct is you would see some really unfortunate covariance - that is, another variable that increases (or decreases) at the same time as microplastics and is known to impact your variable of interest, e.g. socioeconomic status.
Throwing in my $0.02, a correlation study is technically an option, where you look at differences as microplastics increase in concentration. But. my instinct is you would see some really unfortunate covariance - that is, another variable that increases (or decreases) at the same time as microplastics and is known to impact your variable of interest, e.g. socioeconomic status.