New Look’s website improved its overall competitiveness, with the category pages (that were redirected to) outranking the OOS product URLs. Also, the number of keywords that these pages ranked for increased significantly, resulting in an uplift in both revenue and visits.
Due to general competition and fluctuation, rankings shifted towards long-tail keywords, counter-balancing the seasonal drift in rankings of generics.
Since previously sold products can be attributed with value other than their physical ownership (such as the generation of on-site product reviews, design and straightforward site navigation), how to most effectively deal with OOS product pages will depend on the scale of your website and the nature of your business.
Based on the data generated from this project however, when dealing with a large scale ecommerce site, it is highly effective from an SEO perspective to redirect OOS pages to relevant category or product pages with the aid of an overlay explaining the redirection to the user.