1. Experiments Erick Lachapelle University of Montreal This material is distributed under an Attribution-NonCommercial-ShareAlike 3.0 Unported Creative Commons License, the full details of which may be found online here: http://creativecommons.org/licenses/by-nc-sa/3.0/. You may re-use, edit, or redistribute the content provided that the original source is cited, it is for non-commercial purposes, and provided it is distributed under a similar license.http://creativecommons.org/licenses/by-nc-sa/3.0/

2. Lesson Plan What is an experiment? Objectives of experiments How to conduct experiments? Limits of experiments

3. What is an experiment? Experiment involves measuring the effect of manipulation in one of two comparable groups. The manipulation causes variation in one of the independent variables. Experimental conditions allow us to isolate the effect of one independent variable while controlling for other possible influences.

4. Objectives and characteristics of experiments To falsify hypotheses (causal inference). To obtain greater control than in the natural environment. To observe a small effect that is difficult to measure in the natural environment. Experiments can be conducted on any political topic that involves humans. –Sometimes they can also be found in policy evaluation studies.

5. How to conduct experiments? To get access to volunteers who are willing to participate in a serious way. To divide volunteers in at least two groups (experimental group and control group) –By a process of random selection to avoid « allocation bias » To design manipulation –To show creativity. To design artificial environment –If necessary

6. Types of experiments Lab experiments Survey experiments Natural experiments

7. Example #1: The effect of party positions on partisan opinion Question: to what extent is partisan opinion formed independently from the position of the party? H 1 : Partisan opinion depends on the position of the party. H 0 : Partisan opinion is not influenced by the position of the party. Process: –Selection of a sample of party members, who are equally distributed between two opposing parties. Creation of two articles on a project of changing health insurance coverage for the poor: one version about increasing the coverage and the other about reducing it. –Control group: include party members from two parties, which receive a version of an article mentioning that legislators are divided on the project but without stating their positions. –Experimental groups: include members of two parties, which receive an article mentioning that their party is in favour and the opposing party is against or that their party is against and the opposing party is in favour.

8. Results Source: John G. Bullock (2011). « Elite Influence on Public Opinion in an Informed Electorate ». American Political Science Review. 105(3): 496-515.

9. Example #2: The effect of deliberation on political tolerance Question: Do interactions with people who we disagree with make us more tolerant and interactions with those who we agree with make us less tolerant? H 1 : Tolerance of people increases when their opinions are confronted with those of their adversaries and decreases when confirmed by those who share them. H 0 : Tolerance is not affected by the interaction with people holding contrary or similar opinions. Process: –Selection of a sample of people with different opinions on controversial issues, including death penalty, homosexual marriage, prison sentences for repeat offenders... Produce arguments in support of each of the two possible positions on these issues. –Control group: includes people having different opinions and exposed to arguments that are not relevant to these issues. –Experimental groups: include people having a certain point of view and exposed to arguments that refute their position. The other includes people having a certain point of view and exposed to arguments that support their position.

10. Results Source: Diana C. Mutz (2006). Hearing the Other Side: Deliberative versus Participatory Democracy. Cambridge: Cambridge University Press. Pp. 79- 84.

11. Example #3: The effect of mass media on the credibility of experts « Scientists exaggerate the global warming issue in their own interests »

12. Example #4: The effect of images on petroleum moratorium Version A: reassuring images Version B: disturbing images

13. Survey experiment Reassuring images versus disturbing images Are you in favour of banning offshore petroleum exploration? 25% vs 19%75% vs 81%

14. Limits of experiments The illusion of total control Selection bias External validity Ethics Phenomenon Observations reliable, not valid