{"id":133,"date":"2010-05-03T21:00:46","date_gmt":"2010-05-04T04:00:46","guid":{"rendered":"http:\/\/www.mii.ucla.edu\/causality\/?p=133"},"modified":"2015-12-03T20:14:49","modified_gmt":"2015-12-03T20:14:49","slug":"on-mediation-counterfactuals-and-manipulations","status":"publish","type":"post","link":"https:\/\/causality.cs.ucla.edu\/blog\/index.php\/2010\/05\/03\/on-mediation-counterfactuals-and-manipulations\/","title":{"rendered":"On Mediation, counterfactuals and manipulations"},"content":{"rendered":"

Opening remarks <\/strong><\/p>\n

A few days ago, Dan Sharfstein posed a question regarding the “well-defineness” of “direct effects” in situations where the mediating variables cannot be manipulated. Dan’s question triggered a private email discussion that has culminated in a posting by Thomas Richardson and Jamie Robins (below) followed by Judea Pearl’s reply.<\/p>\n

We urge more people to join this important discussion.<\/p>\n

Thomas Richardson and James Robins’ discussion: <\/strong><\/p>\n

Hello,<\/p>\n

There has recently been some discussion of mediation and direct effects.<\/p>\n

There are at least two issues here:<\/p>\n

(1) Which counterfactuals are well defined.<\/p>\n

(2) Even when counterfactuals are well defined, should we include assumptions that identify effects (ie the natural direct effect) that could never be confirmed even in principle by a Randomized Controlled Trial (RCT).<\/p>\n

As to (1) it is clear to most that all counterfactuals are vague to a certain extent and can be made more precise by carefully describing the (quite possibly only hypothetical) intervention you want the counterfactual to represent. For this reason, \u00a0whether you take manipulation or causality as ontologically primary, we need to relate causation to manipulation to clarify and make more precise which counterfactual world we are considering.<\/p>\n

On (2) we have just finished a long paper on the issue, fleshing out considerably an argument I (Jamie) made at the American Statistical Association (in 2005) discussing a talk by Judea on natural (pure and total) direct effects.<\/p>\n

“Alternative Graphical Causal Models and the Identification of Direct Effects”<\/p>\n

It is available at
\nhttp:\/\/www.csss.washington.edu\/Papers\/wp100.pdf<\/a>.<\/p>\n

Here is a brief summary:<\/p>\n

Click here for the full post.<\/a><\/p>\n

Best wishes,<\/p>\n

Jamie Robins \u00a0and Thomas Richardson<\/p>\n

Judea Pearl’s reply:<\/strong><\/p>\n

1.
\nAs to the which counterfactuals are “well defined”, my position is that counterfactuals attain their “definition” from the laws of physics and, therefore, they are “well defined” before one even contemplates any specific intervention. Newton concluded that tides are DUE to lunar attraction without thinking about manipulating the moon’s position; he merely envisioned how water would react to gravitaional force in general.<\/p>\n

In fact, counterfactuals (e.g., f=ma) earn their usefulness precisely because they are not tide to specific manipulation, but can serve a vast variety of future inteventions, whose details we do not know in advance; it is the duty of the intervenor to make precise how each anticipated manipulation fits into our store of counterfactual knowledge, also known as “scientific theories”.<\/p>\n

2.
\nRegarding identifiability of mediation, I have two comments to make; ‘ one related to your Minimal Causal Models (MCM) and one related to the role of structural equations models (SEM) as the logical basis of counterfactual analysis.al basis of counterfactual analysis.<\/p>\n

Click here for Judea’s reply.<\/a>
\n<\/a><\/p>\n

\n

Best regards,<\/p>\n

Judea Pearl<\/p>\n<\/div>\n","protected":false},"excerpt":{"rendered":"

Opening remarks A few days ago, Dan Sharfstein posed a question regarding the “well-defineness” of “direct effects” in situations where the mediating variables cannot be manipulated. Dan’s question triggered a private email discussion that has culminated in a posting by Thomas Richardson and Jamie Robins (below) followed by Judea Pearl’s reply. We urge more people […]<\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[11,29],"tags":[],"class_list":["post-133","post","type-post","status-publish","format-standard","hentry","category-discussion","category-opinion"],"_links":{"self":[{"href":"https:\/\/causality.cs.ucla.edu\/blog\/index.php\/wp-json\/wp\/v2\/posts\/133","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/causality.cs.ucla.edu\/blog\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/causality.cs.ucla.edu\/blog\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/causality.cs.ucla.edu\/blog\/index.php\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/causality.cs.ucla.edu\/blog\/index.php\/wp-json\/wp\/v2\/comments?post=133"}],"version-history":[{"count":2,"href":"https:\/\/causality.cs.ucla.edu\/blog\/index.php\/wp-json\/wp\/v2\/posts\/133\/revisions"}],"predecessor-version":[{"id":1602,"href":"https:\/\/causality.cs.ucla.edu\/blog\/index.php\/wp-json\/wp\/v2\/posts\/133\/revisions\/1602"}],"wp:attachment":[{"href":"https:\/\/causality.cs.ucla.edu\/blog\/index.php\/wp-json\/wp\/v2\/media?parent=133"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/causality.cs.ucla.edu\/blog\/index.php\/wp-json\/wp\/v2\/categories?post=133"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/causality.cs.ucla.edu\/blog\/index.php\/wp-json\/wp\/v2\/tags?post=133"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}