What is the basis for the federal district court's finding that defendants were responsible for between 15 to 50 kilograms of cocaine?

Moreover, the district court's failure to articulate the basis for its conclusion that defendants were responsible for between 15 and 50 kilograms of cocaine makes meaningful appellate review difficult, if not impossible. See United States v. Jewel, 947 F.2d 224, 234 (7th Cir.1991). The amount of cocaine involved in the conspiracy and attributable to each defendant was the subject of much debate at the sentencing proceeding. In response to defense counsel's objections, the sentencing judge explained that he had prepared notes at trial to ascertain the quantity of cocaine but added that he was "not going into the analysis of that." His decision not to reveal the factual basis for the base offense calculation makes it very difficult for us to determine whether the calculation was supported by the evidence.