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Rainfall Insurance and Basis Risk
Professor Tobacman, Li Zheng
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Overview Definition 1 Definition 2 Reality check
Moving Forward: Empirical Studies
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Basis Risk Occurs when Payout from indexed insurance
Actual losses experienced do not match.
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Definition 1 I defined the basis risk facing farmers as:
π΅ππ ππ π
ππ π= π π π 2 | π’ππππ π β πππ π’πππππ ππππππππ π π π 2 | π’ππππ 0 ππππππππ π π is the income of the π π‘β farmer / state
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Definition 1 (Continued)
π¦ π = π π + π π€ +π β + π π π π ~ π(0, π π π 2 ) πΌ π€ = πππ¦ππ’π‘ ππππ πππ ππππππ¦ ππππππ’π π=πΈ πΌ π€ (fair insurance) Variable w here represents the index or indices in question
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Definition 1 (Continued)
Under π insurance policies, π π =ππ΄ π¦ π + π πΌ π€ β π πΈ π π =ππ΄ π π πππ π π = π΄ 2 π 2 π π¦ π π 2 π πΌ(π€) 2 + 2π΄ππ πΆππ£( π¦ π , πΌ π€ ) Here A is the area under farming and p is the price per unit yield. It is expected that πΆππ£ π¦ π , πΌ π <0.
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Definition 1 (Continued)
With CARA Utility, π π π =πΈ π π β 1 2 β
πππ π π = ππ΄ π π β 1 2 β
π΄ 2 π 2 π π¦ π π 2 π πΌ(π€) 2 + 2π΄ππ πΆππ£( π¦ π , πΌ π€ ) β
is the coefficient of risk aversion
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Definition 1 (Continued)
Maximizing utility with respect to π : π(π( π π ) ππ =0β 1 2 β
0+ 2 π β π πΌ(π€) 2 + 2π΄π πΆππ£ π¦ π , πΌ π€ =0 π 2 (π( π π ) π π 2 =2 π πΌ(π€) 2 >0 β π Ο΅ π 0 + π β = β π΄π πΆππ£ π¦ π , πΌ π€ π πΌ π€ 2 For now we are assuming ability to purchase non-discrete amounts of insurance
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Definition 1 (Continued)
Under this definition and the expression for π β : π΅ππ ππ π
ππ π= π π π 2 | π’ππππ π β πππ π’πππππ ππππππππ π π π 2 | π’ππππ 0 ππππππππ = π΄ 2 π 2 π π¦ π (π β ) 2 π πΌ π€ π΄ π β π πΆππ£ π¦ π , πΌ π€ π΄ 2 π 2 π π¦ π 2 =1+ π΄ 2 π 2 π πΌ(π€) 2 [ πΆππ£ π¦ π , πΌ π€ ] 2 π΄ 2 π 2 π π¦ π 2 [ π πΌ π€ 2 ] β2 π΄ 2 π 2 [ πΆππ£ π¦ π , πΌ π€ ] 2 π΄ 2 π 2 π π¦ π 2 π πΌ(π€) 2 =1β πΆππ£ π¦ π , πΌ π€ π π¦ π π πΌ(π€) 2 =1β π π¦ π , πΌ(π€) 2
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Definition 1 (Continued)
Given this specification of basis risk, one has to maximize π π¦ π , πΌ(π€) 2 to minimize basis risk. If we assume that rainfall is independent of all other explanatory variables, we will arrive at one obvious candidate for the functional form of πΌ π€ : πΌ π€ =ππ π€ +π . I will now show that this functional form is indeed one of the candidates that minimizes this definition of basis risk under independence of rainfall.
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Definition 1 (Continued)
Under independence of rainfall: π π¦ π , πΌ(π€) 2 = πΆππ£ π¦ π , πΌ π€ π π¦ π π πΌ(π€) 2 = πΆππ£ π(π€), πΌ π€ π π¦ π π πΌ(π€) 2 = ππΆππ£ π(π€), π(π€) π π π¦ π π π(π€) 2 = π π(π€) 2 π π¦ π π π(π€) 2 = π π(π€) π π¦ π 2 I claim that π π(π€) π π¦ π is the maximum value of π π¦ π , πΌ(π€) 2 .
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Definition 1 (Continued)
Prove by Contradiction:Β If β πΆππ£ π π€ , πΌ π€ π π¦ π π πΌ π€ , π π’πβ π‘βππ‘: πΆππ£ π π€ , πΌ π€ π π¦ π π πΌ π€ > π π π€ π π¦ π 2 πΆππ£ π π€ , πΌ π€ π πΌ π€ > π π π€ 2 πΆππ£ π π€ , πΌ π€ 2 > π π(π€) 2 π πΌ(π€) 2 But this violates the Cauchy-Schwarz Inequality.
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Definition 1 - Assumptions
The above assumes: No interactions between rainfall and other explanatory variables in the model if πΌ π€ =ππ π€ +π is one of the basis risk minimizing insurance models. Using the definition alone allows for interactions between all explanatory variables. CARA utility functions Ability to purchase non-discrete amounts of insurance policies
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Definition 1 β Criticisms
Criticisms of the above definition: Too blunt: Does not isolate basis risk due to rainfall. This definition is a measure of risk due to uncompensated exposure to agriculture as a whole, not due to uncompensated exposure due to rainfall. Too pessimistic: Due to its bluntness, it will likely result in overstated levels of basis risk No clear minimum. It is not clear what the benchmark level of basis risk is, and no clear target to work towards. 0 is unrealistic.
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Definition 1 β Summary What we learnt:
Setting πΌ π€ =ππ π€ +π is one useful functional form that could minimize basis risk.
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Definition 2 To increase precision, I defined basis risk as: π΅ππ ππ π
ππ π= ππππππππ ππ ππππ‘ ππ ππππππ ππ’π π‘π ππππππππ π’ππππ π β πππ π’πππππ ππππππππ ππππππππ ππ ππππ‘ ππ ππππππ ππ’π π‘π ππππππππ π’ππππ 0 ππππππππ = π π π ππ’π π‘π ππππππππ πππ πππππ 2 | π’ππππ π β πππ π’πππππ ππππππππ π π π ππ’π π‘π ππππππππ πππ πππππ 2 | π’ππππ 0 ππππππππ With this definition, basis risk measures risk from unknown and hence uncompensated exposure due to rainfall in agriculture.
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Definition 2 (Continued)
Similarly, we define yield and insurance: π¦ π = π π + π π€ +π β + π π π π ~ π(0, π π π 2 ) πΌ π€ = πππ¦ππ’π‘ ππππ πππ ππππππ¦ ππππππ’π π=πΈ πΌ π€ We now strictly assume that π β πππ π π€ are independent. Other than that there are no restrictions on the functional form of the yield model.
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Definition 2 (Continued)
Intuitively, we expect that all known relationships between rainfall and yield would have been factored into the ideal insurance policy (i.e. compensated). Thus we suspect that: π΅ππ ππ π
ππ π= π π π π π(π€) 2 + π π π 2 Indeed, using similar methods and assumptions as above we arrive at our intuition.
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Definition 2 (Continued)
To increase precision, we only consider income due to contribution of rainfall and unknown factors (error terms). Denote this income as π π
π , and the corresponding yield π¦ π
π Under π insurance policies, π¦ π
π = π π + π π€ +π β + π π =π π€ + π π π π
π =ππ΄ π¦ π
π + π πΌ π€ β π πΈ π π
π =ππ΄πΈ[π π€ ] πππ π π
π = π΄ 2 π 2 π π¦ π
π π 2 π πΌ(π€) 2 + 2π΄ππ πΆππ£( π¦ π
π , πΌ π€ )
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Definition 2 (Continued)
With CARA preferences: π π π
π =πΈ π π
π β 1 2 β
πππ π π
π = ππ΄ π½ π πΈ[π π€ ] β 1 2 β
π΄ 2 π 2 π π¦ π
π π 2 π πΌ(π€) 2 + 2π΄ππ πΆππ£( π¦ π
π , πΌ π€ )
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Definition 2 (Continued)
Maximizing utility by solving for π β : π(π( π π
π ) ππ =0β 1 2 β
0+ 2 π β π πΌ(π€) 2 + 2π΄π πΆππ£ π¦ π
π , πΌ π€ =0 π 2 (π( π π
π ) π π 2 =2 π πΌ(π€) 2 >0 β π Ο΅ π 0 + π β = β π΄π πΆππ£ π¦ π
π , πΌ π€ π πΌ(π€) 2 Again, we ignore discretized purchase requirements in reality.
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Definition 2 (Continued)
Under this definition and the expression for π β : π΅ππ ππ π
ππ π= π π π
π 2 | π’ππππ π β πππ π’πππππ ππππππππ π π π
π 2 | π’ππππ 0 ππππππππ = π΄ 2 π 2 π π¦ π
π (π β ) 2 π πΌ π€ π΄ π β π πΆππ£ π¦ π
π , πΌ π€ π΄ 2 π 2 π π¦ π
π 2 =1+ π΄ 2 π 2 π πΌ(π€) 2 [ πΆππ£ π¦ π
π , πΌ π€ ] 2 π΄ 2 π 2 π π¦ π
π 2 [ π πΌ π€ 2 ] β2 π΄ 2 π 2 [ πΆππ£ π¦ π
π , πΌ π€ ] 2 π΄ 2 π 2 π π¦ π
π 2 π πΌ(π€) 2 =1β πΆππ£ π¦ π
π , πΌ π€ π π¦ π
π π πΌ(π€) 2 =1β π π¦ π
π , πΌ(π€) 2
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Definition 2 (Continued)
It is not unreasonable to assume that all known relationships are modeled into the insurance. Taking the clue from the first definition, we set : πΌ π€ =ππ π€ +π. π΅ππ ππ π
ππ π= 1β πΆππ£ π¦ π
π , πΌ π€ π π¦ π
π π πΌ π€ =1β πΆππ£ π π€ + π π , ππ π€ +π π π π€ + π π π ππ π€ +π 2 = 1β ππΆππ£ π π€ , π π€ π π π π€ π π π π π π€ =1β π π π€ π π π€ π π π π π π€ = 1β π π π€ π π π€ π π π =1β π π π€ 2 π π π€ π π π = π π π π π(π€) 2 + π π π 2 Hence we see that we are back with our intuition.
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Definition 2 - Assumptions
The above assumes: No interactions between rainfall and other explanatory variables in the model. CARA utility functions Ability to purchase non-discrete amounts of insurance policies Although subject to the stricter assumptions as the first definition, we now know that the minimum basis risk is 0.
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Comparison of the 2 Definitions
Definition 1 Definition 2 Pros Probably more relevant to farmers Clear benchmark: 0 Cons No clear benchmark Ignores overall impact on income
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Reality Check If we had defined basis risk to be risk from understood exposure to rainfall, we expect that an insurance model that incorporates this understood exposure to reduce such rainfall risks to zero. π΅ππ ππ π
ππ π = ππππππππ ππ ππππ‘ ππ ππππππ ππ’π π‘π π’πππππ π‘πππ ππππππππ π’ππππ π β πππ π’πππππ ππππππππ ππππππππ ππ ππππ‘ ππ ππππππ ππ’π π‘π π’πππππ π‘πππ ππππππππ π’ππππ 0 ππππππππ = π π π ππ’π π‘π π’πππππ π‘πππ ππππππππ 2 | π’ππππ π β πππ π’πππππ ππππππππ π π π ππ’π π‘π π’πππππ π‘πππ ππππππππ 2 | π’ππππ 0 ππππππππ
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Reality Check Using similar methods as above, defining the income due to understood rainfall as π¦ π
π =π π€ , we arrive at: π΅ππ ππ π
ππ π= 1β πΆππ£ π π€ , πΌ π€ π π π€ π πΌ π€ =0 when we set : πΌ π€ =ππ π€ +π.
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Moving Forward β Empirics
A. Measure Historical basis risk using Definitions 1 and 2 Need data on rainfall and yields APHRODITE data set for rainfall data βIndia Agricultural and Climate Data Setβ (IACDS) prepared by Apurva Sanghi, K.S. Kavi Kumar, and James W. McKinsey, Jr. * Yield modeling With and without interactions Begin with basic forms, then try parametric modeling *The IACDS provides information on agricultural yields and prices for 20 major and minor crops, for each of 270 districts in India, from 1956 to Based on this information, an area-weighted average revenue per unit area was calculated as a proxy for farmerβs revenue per unit area.
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Moving Forward β Empirics
B. Model Historical Basis Risk using current insurance models Start with unitary period model (definitions 1 and 2) Allow for non CARA utility and test robustness of current definitions. Using the growth phase policies from the term sheets, estimate historical basis risk under Ideal π β Discretized ceiling / floor of π β Once theory arrives incorporate multiple phases Compare with basis risk minimizing model of insurance
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Moving Forward β Empirics
C. Model Historical Basis Risk using new insurance models Allow for assumption of non-optimal π β due to demand side factors, test robustness of definitions with respect to π β Allow for non CARA utility
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Summary Stats for Data Statistics / States State 1 State 2 State 3
Mean Rainfall Variance of Rainfall State Mean / Country Mean State Variance / Country Variance Mean Monsoon Rainfall (Area weighted) Mean Monsoon Rainfall (Population weighted) Variance of Monsoon Rainfall Monsoon Start Period Monsoon End Period Major Crops Average Yield (area weighted)
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Models with no Covariates and no Interactions
Model 1 Model 2 Model 3 Model 4 f(w) Linear Quadratic Parametric g(x) Omitted h(w,x) R^2 Basis Risk Definition 1 β n=0 Basis Risk Definition 2 β n=0 Historic Insurance Specification Basis Risk Definition 1 β continuous n* Basis Risk Definition 2 β continuous n* Basis Risk Definition 1 βdiscrete n* Basis Risk Definition 2 β discrete n* Alternative Insurance Specification 1 phases 3 phases
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Models with Covariates and no Interactions
Model 1 Model 2 Model 3 Model 4 f(w) Linear Quadratic g(x) h(w,x) Omitted R^2 Basis Risk Definition 1 β n=0 Basis Risk Definition 2 β n=0 Historic Insurance Specification Basis Risk Definition 1 β continuous n* Basis Risk Definition 2 β continuous n* Basis Risk Definition 1 βdiscrete n* Basis Risk Definition 2 β discrete n* Alternative Insurance Specification 1 phases 3 phases
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Models with Covariate and Interactions
Model 1 Model 2 Model 3 Model 4 f(w) Linear Quadratic g(x) h(w,x) R^2 Basis Risk Definition 1 β n=0 Basis Risk Definition 2 β n=0 Historic Insurance Specification Basis Risk Definition 1 β continuous n* Basis Risk Definition 2 β continuous n* Basis Risk Definition 1 βdiscrete n* Basis Risk Definition 2 β discrete n* Alternative Insurance Specification 1 phases 3 phases
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Summary 2 Definitions of basis risk Moving Forward: Empirics
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Acknowledgments Professor Tobacman for his unending patience, understanding, guidance and support. Professor Cole, Daniel Stein and many more with providence of key data
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