The 400′s of the Texas Rules of Evidence, as well as the Federal Rules of Evidence, deals exclusively with issues relating to relevance. Texas (and federal) rule of evidence 401 is fairly straightforward. If a particular matter has nothing to do with the case being tried a party is not allowed to bring in that evidence.
Where things get more interesting is where something is relevant but is likely to mislead a jury or appeal to a jury’s emotions or biases. Specifically, rule 403 states that evidence may be excluded if its probative value is substantially outweighed by the danger of 1) unfair prejudice, 2) confusion of the issues, or 3) misleading the jury, or by 4) considerations of undue delay, or 5) needless presentation of cumulative evidence.
The Texas rule 403 is different than the federal rule in that it is necessary that the danger of prejudicial evidence substantially outweigh the legitimate value of the evidence. The federal rule only requires that the risk of prejudice outweigh the legitimate value of the evidence. In other words, the Texas rule would seem to permit more borderline evidence to come in under the federal rule. As a practical matter, both rules seem to be applied in a similar manner.