Speakers: Prof. Dr. Rolf Steyer et al.
Summer term 2012, Conference, Course length: 14.25 hours, Language: English, Topic: Analysis of causal effects
Symposium "Causality in Educational Research"
From July 24 to 26, 2012 was held a conference at the "Altes Schloss Dornburg" near Jena.
Aim of the symposium
The symposium is intended to sharpen our ideas and instruments for the analysis of conditional and direct treatment effects. Why does this aim seem to be warranted? In the last decades, analyses of causal effects have mainly focussed on average total effects of treatments. This is appropriate if we are interested in the overall or total effectiveness of treatments in a population of subjects. However, conditional and direct treatment (intervention, exposition) effects are more informative and scientifically more interesting (MacKinnon, 2008).
With conditional total effects we consider the effects of a treatment on an outcome variable given a value of one or more covariates. Such a covariate can be sex, diagnostic group, severity of symptoms before treatment, motivation for treatment, or a multivariate variable consisting of several of such onedimensional variables. Such conditional total effects can differ from each other between different values of the covariates. Hence, with conditional total effects we can quantify the total treatment effects for different (groups of) subjects. How big are the total effects for which kind of subjects? Note that total treatment effects may be positive for some and negative for others. Hence, in clinical research, conditional total effects deal with differential indication of a treatment.
Average and conditional total effects deal with the total effects of a treatment. In contrast, with direct effects we ask for the effects of a treatment that are not transmitted by intermediate variables that, in the process considered, occur up to a specified time point. Controlling for all pretreatment variables and all variables in between treatment and a specified time point of the process, is there still an effect of the treatment? How big are these direct effects on average? How do they differ for different values of the variables controlled? Hence, now we ask: How big are the direct effects for which kinds of subjects? In educational research we may ask if the effects of a teaching method are transmitted to the outcome variable by raising the motivation to learn and by increasing time spent on learning, or if the total effect observed is not mediated through these and other variables occurring in the process up to the time point to which time spent on learning refers.
Asking for direct causal effects of a treatment has gained increasing interest in the last years because it has been shown that the wellknown path analysis procedures for the analysis of direct and indirect effects often lead to systematically wrong results even in the randomized experiment. This is due to the fact that independence of treatment and covariates induced by randomization is cancelled as soon as we condition on an intermediate variable that is affected by treatment and is correlated with a pretreatment variable. In this case, the partial correlation between the treatment variable and the covariate, controlling for the intermediate variable, is not zero. For example, if the intermediate motivation is affected by treatment and it depends on pretreatment motivation, then a high score on intermediate motivation goes along with a high score on treatment (e. g., 1) and a high score on pretreatment motivation, whereas a low score on intermediate motivation goes along with a low score on treatment (e. g., 0) and a low score on pretreatment motivation. Independence of the treatment variable and all pretreatment variables (induced by randomization) implies unbiasedness of mean differences of the outcome variable between treatment groups, but it does not imply unbiasedness of direct effects if we only include treatment, intermediate, and outcome variables in our analysis.
References:
Organizational structure
The structure of the conference was closely followed the "Symposium on Causality 2010". There were 5 focus presentations by leading proponents in different fields of causality research. Each focus presentation was discussed and supplemented by two invited discussants, followed by an open discussion among all participants. There was also be room for participants to present their own research in short presentations.
For further information, please visit the website of the Symposium on Causality 2012.
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Monday, July 23  Tuesday, July 24  Wednesday, July 25  Thursday, July 26  

09:00  09:45 
David MacKinnon "Introduction to Mediation Analysis: Importance, Applications, and Examples" Video 01 with slides Rolf Steyer "The definition of total, direct and indirect effects and their identification" Video 01 with slides 
Kosuke Imai "The potential outcome approach to direct effects: Definition, identification, and sensitivity analysis" Video 05 with slides Stephen West Invited discussion Video 05 with slides 
Felix Thoemmes "Covariate selection for total and direct effects: A comparative view" Video 09 with slides Peter Steiner Invited discussion Video 09 with slides 

09:45  10:15  
10:15  10:45  
10:45  11:15  Coffee break  Coffee break  Coffee break  
11:15  12:30 
Axel Mayer "Identification and estimation of direct and indirect effects" Video 02 with slides General discussion 
General discussion Video 06 with slides 
Johannes Textor "Graphical Approaches to Covariate Selection for Direct and Partial Causal Effects" Video 10 with slides General discussion Video 10 with slides 

12:30  14:15  Lunch  Lunch  Packed lunch at departure instead of lunch  
14:15  15:15 
Short contributions MarieAnn Sengewald "Accounting for fallible covariates  a comparison of ANCOVA and Propensity Score methods" Video 03 with slides Martin Huber "Identifying causal mechanisms in experiments (primarily) based on inverse probability weighting" Video 03 with slides 
Short contributions Ana Kolar "Causal Inference From Small Samples Using Propensity Score Matching Techniques" Video 07 with slides Sonja Hahn "Unbalanced designs containing a qualitative covariate as a factor: Are twoway ANOVA procedures adequate to test a causal hypothesis?" Video 07 with slides Boris Mayer "Conditional Causal Effects in CrossCultural Research: Two Examples using HLM and SEM" Video 07 with slides 

15:15  15:45  Coffee break  Coffee break  
15:45  16:30 
Philip Dawid "A probabilistic approach to direct and indirect effects" Video 04 with slides Andreas Klein "Conceptual difficulties of modeling mediation: Logical and statistical problems intertwined" Video 04 with slides 
Susanne Rässler "Conditional effects: How to use them in practice" Video 08 with slides David Rindskopf Invited discussion Video 08 with slides 

16:30  17:00  
17:00  17:30  
17:30  18:00  General discussion  General discussion  
19:30  Welcome Reception  
20:00  Conference Dinner 