Causal Inference Together With Random Trials

image: Tamil Nadu nutrition study Nancy Cartwright has spent much of her career probing the assumptions scientists brand close causatio...

image: Tamil Nadu nutrition study

Nancy Cartwright has spent much of her career probing the assumptions scientists brand close causation. She has helped to demonstrate that the Humean assumptions close causation that philosophers (including Carl Hempel) carried into twentieth century philosophy of scientific discipline don't come upwards or thence answering the inquiry correctly, as well as she has provided many reasons to accept seriously the ideas of causal powers as well as mechanisms rather than governing causal regularities. How the Laws of Physics Lie is an of import contribution to the philosophy of scientific discipline as well as to realist theory.

Her electrical flow mass Evidence-Based Policy: Influenza A virus subtype H5N1 Practical Guide to Doing It Better (with Jeremy Hardie) provides a dissimilar critical perspective on causal inference, this fourth dimension inwards the context of social policy reasoning. The blueprint as well as implementation of world policies residuum upon a primal premise: that nosotros tin own got evidence-based reasons for predicting what the effects of the policy tool volition probable be. But what variety of bear witness powerfulness that be? The dominant cast of bear witness favored inwards the policy scientific discipline champaign is random controlled trials: specify the policy intervention P, direct a domain of cases to apply the intervention P to, randomly select cases to have the intervention (versus the command grouping that does not), as well as mensurate the value of the outcome of interest. If at that topographic point is a pregnant departure inwards the value of the outcome betwixt exam grouping as well as command group, thence nosotros own got bear witness that P had an effect.

In a nutshell, C&H accept number amongst the conviction that random controlled trials  (RCT) -- the gilded measure of causal inference as well as experiment inwards clinical medicine -- render a soil for expecting that a given policy intervention volition own got similar effects inwards the future. Their mass tin travel read every bit a critique of an excessively statistical agreement of social causality, without realistic analysis of the underlying mechanisms as well as processes. As Cartwright as well as Hardie terra firma repeatedly, RCT bear witness shows solely that the policy worked on the circumstances tested inwards the study. Instead, they fence that nosotros demand to offering bear witness close 2 additional considerations: whether the "causal principle" associated amongst P volition stay the same inwards novel circumstances; as well as whether the associated weather condition necessary for the functioning of this regulation volition travel introduce inwards the novel circumstances.

Here is a primal declaration of what they hateful past times a causal principle:

We suppose that causes exercise non attain their effects past times accident, at to the lowest degree non if you lot are to travel able to brand reliable predictions close what volition direct house if you lot intervene. Rather, if a crusade produces an effect, it does thence because at that topographic point is a reliable, systematic connection betwixt the two, a connection that is described inwards a causal principle. (22)

The statement, "El Nino causes moisture winters inwards North America," is a causal principle. But causal principles are neither universal nor exceptionless:

The fact that causal principles tin differ from locale to locale agency that you lot cannot read off that a policy volition piece of occupation hither from fifty-fifty real solid bear witness that it worked somewhere else. (23)

Here is a to a greater extent than extensive description of this idea:

Causal principles are non universal. They differ from house to house as well as from fourth dimension to time. That agency that it is non plenty for you lot to know that the policy worked somewhere or fifty-fifty that it has worked at some fourth dimension here. “It worked there”; it played a positive causal piece of occupation there. So it was 1 of the factors from a causal regulation that holds there. To predict that it volition piece of occupation here, you lot demand to know that it is 1 of the factors from a causal regulation that holds here. That is what ensures that it tin play a positive causal piece of occupation for you. (50)

Cartwright as well as Hardie facial expression at causation along the lines of J. L. Mackie's analysis of INUS weather condition inwards The Cement of the Universe: a ingredient is a crusade if it is an "Insufficient only Necessary business office of an Unnecessary only Sufficient status for producing a contribution to the effect" (23). The bear witness of favorable CRT studies for a given policy intervention doesn't present that this policy volition piece of occupation inwards the novel circumstances of the novel proposed application. In monastic say to push clitoris this inference nosotros demand to own got confidence that the handling volition play the same causal piece of occupation inwards the novel setting, as well as that the necessary weather condition volition travel introduce inwards that setting. In other words, nosotros demand a to a greater extent than detailed causal analysis of the past times as well as the proposed future.

Here is a sketch of the declaration that C&H suggest nosotros demand to render inwards monastic say to projection favorable RCT studies onto hereafter applications:

1. x industrial plant at that topographic point (i.e., x truly appears inwards the causal regulation that governs the production of y at that topographic point post-implementation). 
2. Here as well as at that topographic point part that causal regulation post-implementation. 
3. The back upwards factors necessary for x to contribute nether that regulation are introduce for at to the lowest degree some individuals hither post-implementation. 
4. Conclusion. x industrial plant hither (i.e., x truly appears inwards the causal regulation that governs the production of y hither post-implementation as well as the back upwards factors necessary for it to contribute to y are introduce for at to the lowest degree some individuals hither post-implementation). (41)

One way of offering back upwards for premise 2 is to engage inwards the method of process tracing:

This method confirms the beingness of a causal connection betwixt get as well as complete past times confirming, one-by-one, a serial of smaller causal steps inwards between. (38)

Cartwright doesn't seat her illustration inwards these terms, only I would say that the view of her intuition is that social outcomes are dissimilar from medical outcomes because of their inherent causal heterogeneity. In the social soil outcomes similar teen pregnancy rates or high schoolhouse dropout rates are the final result of a packet of conjunctural causal processes. So projecting the results of past times random controlled trials into the hereafter requires that nosotros showtime confirm that the same causal influences as well as of import background weather condition are at work. And this is rarely the case. So the primal underlying prescription is a pragmatic causal realism close social processes: inwards monastic say to blueprint as well as implement policies, nosotros demand to own got a good developed map of the existent causal processes as well as mechanisms that are underway inwards the production of the lawsuit nosotros would similar to change. In other words, nosotros demand to travel causal realists if nosotros are to travel effective policy makers.

(It is worth observing that this mass is deliberately dissimilar inwards musical note as well as specialization from Cartwright's other monographs inwards the philosophy of causation. The mass is designed to travel useful for existent practitioners of world policy, as well as it offers clear advice close how to gain the understandings needed inwards monastic say to validate the persuasion that a given policy volition own got desired effects inwards a novel setting.)