Groupthink: Theory and Evidence

Transcription

1 Groupthink: Theory and Evidence ETHZ, Game Theory and Society, July 27-30, 2011 Christopher Baker Harvard University Hanja Blendin & Gerald Schneider Universität Konstanz

2 Motivation Thomas C. Schelling 2006, An astonishing 60 years: The legacy of Hiroshima [Nobel Prize Lecture]: The most spectacular event of the past half century is one that did not occur. We have enjoyed 60 years without nuclear weapons exploded in anger....we may come to a new respect for deterrence

3 What is groupthink?

4 The Decision to Invade Iraq Senator Pat Roberts, Chairman of the U.S. Senate Intelligence Committee, the intelligence community was suffering from what we call a collective groupthink C=Conceding D=Demand Source: F. Zagare Reconciling Rationality with Deterrence. Journal of Theoretical Politics

5 Definition of Groupthink: A mode of thinking that people engage in when they are deeply involved in a cohesive in-group, when the members' strivings for unanimity override their motivation to realistically appraise alternative courses of action. (Janis 1972, 9) Problems:

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7 Problems - Many citations (>2500), few recent experimental tests - Limited microfoundations Our approach - Formal model of groupthink - Focus on stress and cohesion Source: Parks (2000)

8 Antecedents Black box Decision Disaster Stress Group cohesion Deflated selfconfidence Concurrence seeking Reduced decision quality

9 The theoretical foundations: an adapted version of the Condorcet Jury Voting Model Condorcet Jury Theorem: If the probability of voting for the right decision exceeds 0.5, then larger groups make a more correct version than smaller ones. Austen-Smith/Banks (1996) and Feddersen/Pesendorfer (1998) show how strategic voting undermines this optimism. We use the latter model to show some conditions under which irrational believes lead to concurrence seeking and poor decisions.

10 Crisis cabinet of a country (Janistan) has to decide if to escalate in a conflict or not Correct decision depends on the opponent (Whyteland) Outcome(decision = escalate Whyteland = hostile) = 0 O(e H ) = q O(e H ) = 0 O(e H ) = (1 q) q = members escalation threshold Probability that signal is correct: Probability that signal is wrong: Pr(s i = h H ) = Pr(s i = h H ) = c Pr(s i = h H ) = Pr(s i = h H ) = 1 c

11 Assumptions -1- ministers have identical competence levels -2- ministers update their beliefs based on information of the others -3- prime minister casts his/her vote first, the others then simultaneously -4- prime minister votes informatively, this is common knowledge Equilibria unique symmetric response equilibrium: i votes informatively, when pessimistic mixed strategy for optimistic mixed strategy for β( ˆk 1,n) q < β( ˆk,n) 0 < σ(s i = h ) < σ(s i = h) = 1 0 = σ(s i = h ) < σ(s i = h) < 1

12 Variation 1: expected competence of leader exceeds actual competence c 1 > c i 1 Equilibrium ranges between: always copying the prime minister s vote and the equilibrium of the base scenario Variation 2: Ministers are under-confident c > c i The smaller c i the more a minister tends to ignore the own signal and to copy the prime minister s vote

13 Experiment Conducted 2010 in the lakelab of the University of Konstanz (programmed in z-tree) 104 subjects of all faculties, mainly males 2(3) treatments: time pressure, cohesion 3 dependent variables - concurrence seeking (change of opinion after decision) - self-confidence after knowledge test - wrong decisions (100 balls in jar, guessing the dominant color)

14 Of which color are there more balls in the jar?

15 Time pressure increases concurrence-seeking Cohesion (in the form of building team and participation in rock-scissor game) decreases self-confidence Table 1: Influence of treatments on concurrence-seeking (CS) and self-confidence (SC) CS (1) CS(2) CS(3) SC (4) SC (5) SC (6) Time pressure 1.8* 3.33* (0.78) (2.38) (0.26) (1.29) Cohesion *** 0.44 (0.54) (1.39) (0.11) (0.26) Cohesion and time pressure 0.38 (0.35) 0.17* (0.17) Log-Likelihood % correctly predicted Notes: N=104. Coefficients are odds ratios, standard error in parentheses. * p < 0.10, ** p < 0.05, *** p<0.01

16 Time pressure and self-confidence decrease decision making quality Cohesion increases quality of decisions Table 2: Influence of treatments, of concurrence seeking and of self-confidence on decisio quality (DQ) Time pressure Cohesion Cohesion and time pressure Concurrence seeking Concurrence seeking and time pressure Self-confidence (1) ( 2) (3) (4) (5) 0.40** 2.05 (0.18) (1.41) ** (0.76) (2.76) 0.04*** (0.05) 0.86 ( *** (0.10) 0.36 (0.23) 13.49** (13.98) 0.56 (0.24) 0.06*** (0.05) 0.18*** (0.12) 18.26*** (19.31) Self-confidence and time pressure Log-Likelihood % correctly predicted

17 BBS version of CJT provides one mechanism through which groupthink and the consequences of groupthink might be explained Time pressure increases concurrence-seeking and decreases decision making quality Concurrence seeking results more ambiguous: Cohesion increases self-confidence and not confidence in group, increased self-confidence lowers decision making quality

18 Appendix β(k, n) = c k (1 c) n k c k (1 c) n k + c n k (1 c) k i always votes informatively when: β( ˆk 1,n) q < β( ˆk,n)

19 Pessimistic mixed strategy (1 %c) n ˆk +1 (1 %c) n ˆk +1 + %c < q < β( ˆk 1,n) n ˆk +1 Unique symmetric equilibrium in mixed strategies such that: σ 1 (h) = σ i 1 (v 1 = e, s 1 = h) = σ i 1 (v 1 = e, s 1 = h) = 1 σ 1 (h ) = σ i 1 (v 1 = e, s 1 = h ) = σ i 1 (v 1 = e,s 1 = h ) = v * The probability that i votes for escalate is between v* and < v* = %c(1+ A k 1 ) 1 1 k 1 %c A (1 %c) < 1, with A = (1 q)(1 %c)n k +1 n k +1 q%c Pessimistic strategy

20 Mixed strategy c k β( ˆk,n) < q < c k + (1 c) k Unique symmetric equilibrium in mixed strategies such that: σ 1 (h) = σ i 1 (v 1 = e,s 1 = h) = σ i 1 (v 1 = e,s 1 = h) = w * σ 1 (h ) = σ i 1 (v 1 = e, s 1 = h ) = σ i 1 (v 1 = e, s 1 = h ) = 0 The probability that i chooses escalate is between 0 and w* 0 = σ(s i = h ) < σ(s i = h) < 1 Optimistic strategy