{"id":570,"date":"2018-04-16T08:30:00","date_gmt":"2018-04-16T12:30:00","guid":{"rendered":"http:\/\/darwin.eeb.uconn.edu\/uncommon-ground\/?p=570"},"modified":"2018-04-15T14:04:30","modified_gmt":"2018-04-15T18:04:30","slug":"causal-inference-in-ecology-counterfactuals","status":"publish","type":"post","link":"https:\/\/darwin.eeb.uconn.edu\/uncommon-ground\/blog\/2018\/04\/16\/causal-inference-in-ecology-counterfactuals\/","title":{"rendered":"Causal inference in ecology &#8211; Counterfactuals"},"content":{"rendered":"<p><a href=\"http:\/\/darwin.eeb.uconn.edu\/uncommon-ground\/causal-inference-in-ecology\/\">Causal inference in ecology &#8211; links to the series<\/a><\/p>\n<p>Let\u2019s start with a few preliminaries.<sup><a id=\"ffn1\" href=\"#fn1\" class=\"footnote\">1<\/a><\/sup><\/p>\n<ul>\n<li>A <em><strong>causal factor<\/strong><\/em> (\u201ccause\u201d for short) is something that is predictably related to a particular outcome. For example, fertilizing crops generally increases their yield, so fertilizer is a causal factor related to yield. The way I think about it, a causal factor need not always lead to the outcome. It\u2019s enough if it merely increases the probability of the outcome. For example, smoking doesn\u2019t always lead to lung cancer among those who smoke, but it does increase the probability that you will suffer from lung cancer if you smoke.<\/li>\n<li><em><strong>Causes precede effects<\/strong><\/em>.<sup><a id=\"ffn2\" href=\"#fn2\" class=\"footnote\">2<\/a><\/sup> That\u2019s one reason why <a href=\"https:\/\/en.wikipedia.org\/wiki\/Teleology\">teleology<\/a> is problematic. A teleological explanation explains the current state of things as a result of, i.e., as caused by, something in the future, namely a purpose.<sup><a id=\"ffn3\" href=\"#fn3\" class=\"footnote\">3<\/a><\/sup><\/li>\n<li><em><strong>Effects may have multiple causes<\/strong><\/em>. The world, or at least the world of biology, is a complicated place. Regardless of what phenomenon you\u2019re studying, there are likely to be several (or many) causal factors that influence.<\/li>\n<\/ul>\n<p>The last point is one of the most important ones for purposes of this series. When we are investigating a phenomenon,<sup><a id=\"ffn4\" href=\"#fn4\" class=\"footnote\">4<\/a><\/sup> we\u2019re trying to discern which of several plausible causal factors plays a role and, possibly, the relative \u201cimportance\u201d of those causal factors.<sup><a id=\"ffn5\" href=\"#fn5\" class=\"footnote\">5<\/a><\/sup> <\/p>\n<p>To make this concrete, let\u2019s suppose that we\u2019re trying to determine whether application of nitrogen fertilizer increases the yield of corn. That means we have to determine whether adding nitrogen <em><strong>and adding nitrogen alone<\/strong><\/em> increases corn yield. Why the emphasis on \u201cadding nitrogen alone\u201d? Suppose that we added nitrogen to a corn field by adding manure. Then increases in the amount of applied nitrogen are associated with increases in the amount of a host of other substances. If yields increased, we\u2019d know that adding manure increases yield, but not whether it\u2019s because of the nitrogen in manure or something else. Why does this matter?<\/p>\n<p>From very early on in our education we\u2019re taught that \u201ccorrelation is not the same as causation.\u201d We want to distinguish cases where A <em><strong>causes<\/strong><\/em> B from cases where A is merely <em><strong>correlated<\/strong><\/em> with B. Yet, as David Hume pointed out long ago, experience<sup><a id=\"ffn6\" href=\"#fn6\" class=\"footnote\">6<\/a><\/sup> alone can only show us that A and B <em><strong>actually<\/strong><\/em> occur together, not that they <em><strong>must<\/strong><\/em> occur together (<a href=\"http:\/\/www.iep.utm.edu\/hume-cau\/\">link<\/a>).  One way of distinguishing cause from correlation is that causes support counterfactual statements. They provide us with a reason to believe statements like \u201cIf we had applied nitrogen to the field, the corn yield would have increased\u201d even if we never applied nitrogen to the field at all. The only reason I can see that we could believe such a statement is if we had already determined that adding nitrogen <em><strong>and adding nitrogen alone<\/strong><\/em> increases corn yield.<sup><a id=\"ffn7\" href=\"#fn7\" class=\"footnote\">7<\/a><\/sup><\/p>\n<p>How do we determine that? Randomized controlled experiments are the most widely known approach, and they are typically regarded as the gold standard against which all other means of inference are compared. That\u2019s where we\u2019ll pick up in the next installment.<\/p>\n<ol id=\"footnotes\">\n<li id=\"fn1\">As I warned in the introduction to the series, I am not an expert in causal inference. The terminology I use is likely both to be imprecise and to be somewhat different from the terminology experts use. <a href=\"#ffn1\">&#8617;<\/a><\/li>\n<li id=\"fn2\">Philosophers have argued about whether <a href=\"https:\/\/plato.stanford.edu\/entries\/causation-backwards\/\">backward causation<\/a> is possible, but I\u2019m going to ignore that possibility. <a href=\"#ffn2\">&#8617;<\/a><\/li>\n<li id=\"fn3\">Biologists sometimes use teleological language to explain adaptation, e.g., land animals evolved legs to provide mobility. It is, however, relatively easy (if a bit long-winded) to eliminate the teleological language, because natural selection shows how adaptations arise from differential reproduction and survival (<a href=\"https:\/\/en.wikipedia.org\/wiki\/Teleology_in_biology\">link<\/a>).  <a href=\"#ffn3\">&#8617;<\/a><\/li>\n<li id=\"fn4\">Or at least this is how it is when <em><strong>I\u2019m<\/strong><\/em> investigating a phenomenon. <a href=\"#ffn4\">&#8617;<\/a><\/li>\n<li id=\"fn5\">I\u2019ll come back to the idea of identifying the relative importance of causal factors in a future post. <a href=\"#ffn5\">&#8617;<\/a><\/li>\n<li id=\"fn6\">Or experiment. <a href=\"#ffn6\">&#8617;<\/a><\/li>\n<li id=\"fn7\">If there are any philosophers reading this, you\u2019ll recognize that this account is horribly sketchy and amounts to little more than proof by vigorous assertion. If you\u2019re so inclined, I invite you to flesh out more complete explanations for readers who are interested. <a href=\"#ffn7\">&#8617;<\/a><\/li>\n<\/ol>\n","protected":false},"excerpt":{"rendered":"<p>Causal inference in ecology &#8211; links to the series Let\u2019s start with a few preliminaries.1 A causal factor (\u201ccause\u201d for short) is something that is predictably related to a particular&#8230; <a class=\"read-more-button\" href=\"https:\/\/darwin.eeb.uconn.edu\/uncommon-ground\/blog\/2018\/04\/16\/causal-inference-in-ecology-counterfactuals\/\">Read more &gt;<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[10],"tags":[],"class_list":["post-570","post","type-post","status-publish","format-standard","hentry","category-statistics"],"_links":{"self":[{"href":"https:\/\/darwin.eeb.uconn.edu\/uncommon-ground\/wp-json\/wp\/v2\/posts\/570","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/darwin.eeb.uconn.edu\/uncommon-ground\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/darwin.eeb.uconn.edu\/uncommon-ground\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/darwin.eeb.uconn.edu\/uncommon-ground\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/darwin.eeb.uconn.edu\/uncommon-ground\/wp-json\/wp\/v2\/comments?post=570"}],"version-history":[{"count":2,"href":"https:\/\/darwin.eeb.uconn.edu\/uncommon-ground\/wp-json\/wp\/v2\/posts\/570\/revisions"}],"predecessor-version":[{"id":572,"href":"https:\/\/darwin.eeb.uconn.edu\/uncommon-ground\/wp-json\/wp\/v2\/posts\/570\/revisions\/572"}],"wp:attachment":[{"href":"https:\/\/darwin.eeb.uconn.edu\/uncommon-ground\/wp-json\/wp\/v2\/media?parent=570"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/darwin.eeb.uconn.edu\/uncommon-ground\/wp-json\/wp\/v2\/categories?post=570"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/darwin.eeb.uconn.edu\/uncommon-ground\/wp-json\/wp\/v2\/tags?post=570"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}