Links and Brand as Ranking Factors: 2021 Correlation Study

Moz published a comprehensive correlation study examining the relationship between various SEO factors and Google rankings across a large dataset of search results. The 2021 edition of this long-running research series provided updated insights into the relative importance of links, brand signals, and on-page factors in Google's ranking algorithm.

Link Factors Remain Significant

The study confirmed that link-based metrics continue to show meaningful correlation with rankings. Page-level link authority and domain-level link metrics both demonstrated positive correlations with higher rankings. However, the research noted that the strength of these correlations has decreased over time as Google incorporates more diverse signals into its algorithm.

Brand Signals Growing in Importance

Branded search volume emerged as one of the strongest correlating factors in the study. Sites with higher branded search demand tended to rank better across both branded and non-branded queries. This suggests that Google increasingly uses brand strength as a quality signal, rewarding sites that have built genuine audience recognition and demand.

Content and Engagement Metrics

The research examined various content factors including word count, readability, and topical depth. While content quality is difficult to measure directly through correlation studies, longer content showed positive but modest correlation with rankings. The study authors cautioned against interpreting this as causation, noting that comprehensive content tends to accumulate more links and engagement naturally.

Limitations and Interpretation

Moz emphasized that correlation studies cannot prove causation and that Google's algorithm includes hundreds of factors beyond what can be measured externally. The value of such research lies in identifying broad patterns and challenging assumptions rather than prescribing specific tactics. Rankings depend on context, competition, and query intent in ways that aggregate correlation data cannot capture.

Source: Moz Blog