Covariates like age, sex, and brain size are often used in brain research to account for other factors that could affect the results. A study looked at recent brain studies and found that different covariates were used in different studies. They then tested how adding these covariates changed the results in brain scans. They found that some covariates didn't change the results much, but others made a big difference. This means researchers need to be careful when choosing which covariates to use in their studies to make sure their results are accurate.