A clinical research team performs a meta-analysis of seven randomized controlled trials comparing Drug X to placebo for prevention of ischemic stroke. The forest plot shows individual study odds ratios (ORs) ranging from 0.6 to 1.2, with a pooled OR of 0.8 (95% confidence interval [CI], 0.6–1.0) represented by a diamond at the bottom. The I² statistic is reported as 75%. Which of the following best describes what the I² value indicates?