Substantial Influence on Trial Errors
The appropriate standard of harm is to disregard an error unless a substantial right has been affected. Tex. Rule App. P. 44.2(b).
In Kotteakos v. United States, 328 U.S. 750, 90 L. Ed. 1557, 66 S. Ct. 1239 (1945), the Supreme Court explained:
If, when all is said and done, the conviction is sure that the error did not influence the jury, or had but very slight effect, the verdict and the judgment should stand, except perhaps where the departure is from a constitutional norm or a specific command of Congress.
But if one cannot say, with fair assurance, after pondering all that happened without stripping the erroneous action from the whole, that the judgment was not substantially swayed by the error, it is impossible to conclude that substantial rights were not affected.
The inquiry cannot be merely whether there was enough to support the result, apart from the phase affected by the error.
It is rather, even so, whether the error itself had substantial influence.
If so, or if one is left in grave doubt, the conviction cannot stand. Kotteakos, 328 U.S. at 764-65.