Effect of statins on plaque volume. Squares to the left of the vertical line indicate regression of coronary plaques, whereas squares to the right of the vertical line indicate progression of coronary plaques. The horizontal line through each square represents the 95% confidence interval (CI). The diamond represents the pooled effect (width of the diamond indicates the 95% CI). Abbreviations: ACS, acute coronary syndrome; SAP, stable angina pectoris.