You will be shown an abstract from a research paper, and a corresponding research question. Determine the answer to the research question based on the context provided. Your answer should be one of: "YES", "NO", or "MAYBE".

Context:
(PURPOSE) The purpose of this paper is to evaluate the efficacy of ultrasonographic screening for primary hepatocellular carcinoma.
(PATIENTS AND METHODS) A total of 680 eligible cases were classified into three groups (surveillance, opportunistic, and symptomatic groups) according to their initial exposure. We used survival time, tumor morphology, and T staging as prognostic outcomes. The outcomes of screened/unscreened and sur veillance/nonsur veillance were compared with the use of the logistic regression model.
(RESULTS) The adjusted odds ratios for the screened group versus the unscreened group, with 1-, 2-, and 3-year survival time being used as outcomes, were 0.33 (95% confidence interval [CI], 0.21-0.52), 0.33 (95% CI, 0.21-0.53), and 0.37 (95% CI, 0.23-0.61), respectively. The adjusted odds ratios for surveillance versus nonsurveillance were 0.58 (95% CI, 0.35-0.97), 0.45 (95% CI, 0.27-0.74), and 0.44 (95% CI, 0.26-0.73). The odds ratios were even smaller when tumor morphology or T stage was taken as the main outcome. All these results were statistically significant. There were significant gradient relationships between prognostic outcomes and extent of screening history.

Question:
Does screening or surveillance for primary hepatocellular carcinoma with ultrasonography improve the prognosis of patients?

Answer:
YES