{"id":5147,"date":"2025-07-14T07:40:34","date_gmt":"2025-07-14T06:40:34","guid":{"rendered":"https:\/\/pcool.dyndns.org\/?page_id=5147"},"modified":"2025-07-14T12:08:04","modified_gmt":"2025-07-14T11:08:04","slug":"immortal-time-bias","status":"publish","type":"page","link":"https:\/\/pcool.dyndns.org\/index.php\/immortal-time-bias\/","title":{"rendered":"Immortal Time Bias"},"content":{"rendered":"\n<p><a href=\"https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC8478821\/\" data-type=\"link\" data-id=\"https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC8478821\/\" target=\"_blank\" rel=\"noreferrer noopener\">Immortal time bias<\/a> occurs when subjects are grouped together on a risk factor that is <strong>unknown at the start<\/strong>, but identified later. During the time from the start of the study to exposure to the risk factor, the subjects are &#8216;immortal&#8217;. For example, the pope and eminent people exceed national life expectancy. Oscar winners outlive other performers.<\/p>\n\n\n\n<p>In orthopaedics, an example is early vs delayed surgery for <a href=\"https:\/\/boneandjoint.org.uk\/Article\/10.1302\/0301-620X.101B9.BJJ-2019-0295.R1\" data-type=\"link\" data-id=\"https:\/\/boneandjoint.org.uk\/Article\/10.1302\/0301-620X.101B9.BJJ-2019-0295.R1\" target=\"_blank\" rel=\"noreferrer noopener\">hip fractures<\/a>. Results are biased as patients who had delay in surgery likely were likely unfit and required optimisation.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"576\" src=\"https:\/\/pcool.dyndns.org\/wp-content\/uploads\/2025\/07\/immortal_time_bias-1024x576.png\" alt=\"\" class=\"wp-image-5204\" srcset=\"https:\/\/pcool.dyndns.org\/wp-content\/uploads\/2025\/07\/immortal_time_bias-1024x576.png 1024w, https:\/\/pcool.dyndns.org\/wp-content\/uploads\/2025\/07\/immortal_time_bias-300x169.png 300w, https:\/\/pcool.dyndns.org\/wp-content\/uploads\/2025\/07\/immortal_time_bias-768x432.png 768w, https:\/\/pcool.dyndns.org\/wp-content\/uploads\/2025\/07\/immortal_time_bias-1536x864.png 1536w, https:\/\/pcool.dyndns.org\/wp-content\/uploads\/2025\/07\/immortal_time_bias.png 1920w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n\n\n\n<p>It is possible to correct for immortal time bias and methods are described <a href=\"https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC8478821\/\" data-type=\"link\" data-id=\"https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC8478821\/\" target=\"_blank\" rel=\"noreferrer noopener\">here<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Immortal time bias occurs when subjects are grouped together on a risk factor that is unknown at the start, but identified later. During the time from the start of the study to exposure to the risk factor, the subjects are &#8216;immortal&#8217;. For example, the pope and eminent people exceed national life expectancy. Oscar winners outlive [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"inline_featured_image":false,"footnotes":""},"class_list":["post-5147","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/pcool.dyndns.org\/index.php\/wp-json\/wp\/v2\/pages\/5147","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pcool.dyndns.org\/index.php\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/pcool.dyndns.org\/index.php\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/pcool.dyndns.org\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/pcool.dyndns.org\/index.php\/wp-json\/wp\/v2\/comments?post=5147"}],"version-history":[{"count":2,"href":"https:\/\/pcool.dyndns.org\/index.php\/wp-json\/wp\/v2\/pages\/5147\/revisions"}],"predecessor-version":[{"id":5205,"href":"https:\/\/pcool.dyndns.org\/index.php\/wp-json\/wp\/v2\/pages\/5147\/revisions\/5205"}],"wp:attachment":[{"href":"https:\/\/pcool.dyndns.org\/index.php\/wp-json\/wp\/v2\/media?parent=5147"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}