Do big losses in judgmental adjustments affect experts behaviour? Fotios Petropoulos, Robert Fildes and Paul Goodwin

Transcription

1 D big lsses in judgmental adjustments affect experts behaviur? Ftis Petrpuls, Rbert Fildes and Paul Gdwin

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3 Mtivatin [Smith et al., 2009, MnSc] Pker players tend t change their behaviur after winning r lsing big pts: Big wins lead t a less aggressive playing behaviur. Big lsses are fllwed by playing less cautiusly. The empirical results supprt the break-even hypthesis and, secndarily, the gambler s fallacy. Dyle Bransn s rush pker strategy is nt fund t be applied in practice. At the same time, behaviural theries such as huse mney and revised assessment are nt supprted. Can we link these insights t judgmental adjustments fr frecasting?

4 Theries and Research Questins Break-even hypthesis: Balancing-ut the effects f judgmental adjustments t crrect the inventry signals. A judgmental adjustment that led t a big lss will be fllwed by anther equally large adjustment in the ppsite directin. Gambler s fallacy: It will happen this time (because it is verdue)! A judgmental adjustment that led t a big lss will be fllwed by anther equally large adjustment in the same directin. RQ1 Des experts behaviur change after big lsses? RQ2 If yes, what can we d t turn this t ur benefit?

5 Types f judgmental adjustments Wrng Directin Actuals (X). Mdel Frecast (MF) r Statistical Frecast r System Frecast. Expert Frecast (EF) r Judgmental Adjustment. This is usually used as the Final Frecast (FF).

6 Types f judgmental adjustments Undersht Actuals (X). Mdel Frecast (MF) r Statistical Frecast r System Frecast. Expert Frecast (EF) r Judgmental Adjustment. This is usually used as the Final Frecast (FF).

7 Types f judgmental adjustments Oversht Actuals (X). Mdel Frecast (MF) r Statistical Frecast r System Frecast. Expert Frecast (EF) r Judgmental Adjustment. This is usually used as the Final Frecast (FF).

8 Hw are big lsses defined? We define: Difference between frecasts Actual difference f statistical estimate and real utcme Prperties f : scale- and directin-free measure fr identifying the type and the magnitude f a judgmental adjustment. Type f adjustment Value f β XL Oversht β > 3 L Oversht 2 < β 3 Oversht 1 < β 2 Undersht 0 < β < 1 Wrng Directin -1 β < 0 L Wrng Directin β < -1 Big Lsses

9 Database and measuring accuracy Mnthly sales f SKUs (pharma prducts). [Franses & Legerstee, 2009, IJF] We cnsider the 774 series where the triplet X, MF, EF is available fr all bservatins. X MF EF Average Relative Mean Abslute Errr: [Davydenk & Fildes, 2013, IJF]

10 Analysis f all judgmental adjustments ARMAE Sample: Only 49% f the adjustments lead t imprvements 25.4% f the adjustments lead t big lsses

11 Analysis f judgmental adjustments after big lss ARMAE Sample: Less than 44% f the adjustments lead t imprvements 1/3 f the adjustments lead t big lsses

12 Analysis f judgmental adjustments after big lss After an XL versht After a L wrng directin After a big lss Adjustments after a big lss are mre prbable t be f the same type and/r the same directin.

13 Crrecting frecasters behaviur Guidance and restrictiveness thrugh FSSs: [Fildes et al., 2009, IJF] Prvide autmated advices that wuld prevent the frecaster frm making adjustments after big lsses. Apply a lck-ut, meaning nt allwing the frecaster t perfrm changes n the statistical frecast after big lsses. Adjusting the adjustments: [Franses & Legerstee, 2011, ESwA] Fr : Damping the judgmental adjustments: the Blattberg-Hch apprach (50% mdel + 50% manager) [1990, MnSc]

14 Imprving the frecasting perfrmance ARMAE After big lsses After L wrng directin After XL vershts Overall Current Practice Guidance* Restrictiveness Blattberg-Hch * assuming that in 50% f the cases the adjustment was prevented. The Blattberg-Hch apprach wrks fr almst 2/3 f the cases after big lsses, a percentage which is higher than the general case. Accuracy imprvements f up t 16% after big lsses.

15 Cnclusins We examined the behaviur f frecasters after big lsses : The prbability f perfrming an adjustment that leads t a big lss increases by 29%. At the same time the prbability f making an adjustment in the same directin is even higher, giving supprt t the gambler s fallacy thery. Simple crrectin strategies can be applied t imprve the frecasting perfrmance: imprvement f up t 16% fr the perids after big lsses. Finally, we defined a new measure t identify the type and magnitude f a judgmental interventin.

16 Next steps Further explre the differences between psitive and negative adjustments (rule-based crrectins n the adjustments?). Explre mre sphisticated strategies fr adjusting the adjustments: Use errr btstrap rules. [Fildes et al., 2009, IJF] Crrelate the applied weights with experts experience and/r behaviur ver multiple lags. [Franses & Legerstee, 2011, ESwA] Examine if autmatically adjusting the adjustments leads the frecasters t change their behaviur in perfrming judgmental interventins. Explre experts behaviur after big wins.

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