An allegation that an affidavit is a sham generally arises when a party presents an affidavit made in bad faith or for purposes of delay. Tex. R. Civ. Proc. 166a(h). Generally, sham affidavits are used to avoid summary judgment. The affidavit constitutes a sham when the affidavit directly contradicts the affiant's deposition testimony. Cantu v. Peacher, 53 S.W.3d 5, 10 (Tex. App.--San Antonio 2001, pet. denied). A trial court may not consider statements included within a sham affidavit. Cantu, 53 S.W.3d at 10-11. It is well established that deposition testimony does not control over conflicting testimony presented by affidavit. Randall v. Dallas Power & Light Co., 752 S.W.2d 4, 5 (Tex. 1988). In Cantu v. Peacher, the Court explained that the differences in witness affidavits and depositions, in sham affidavit complaints, are generally "more a matter of degree and details than direct contradiction." An appellate evaluation requires an analysis of these differences. Cantu, 53 S.W.3d at 10. "We conclude that a court must examine the nature and extent of the differences in the facts asserted in the deposition and the affidavit. If the differences fall into the category of variations on a theme, consistent in the major allegations but with some variances of detail, this is grounds for impeachment, and not a vitiation of the later filed document. If, on the other hand, the subsequent affidavit clearly contradicts the witness's earlier testimony involving the suit's material points, without explanation, the affidavit must be disregarded and will not defeat the motion for summary judgment." Id. at 10-11.