Lettera da Lhasa numero 73. Comportamento di Giffen in Cina
by Roberto Scaruffi
Jensen, R. T., and N. H. Miller, Giffen Behavior: Theory and Evidence, Working Paper 13243, NBER, Cambridge, MA, USA, July 2007,
http://papers.nber.org/papers/W13243
(Jensen, July 2007).
Robert T. Jensen
Nolan H. Miller
Il comportamento di Giffen è correntemente chiamano, in italiano, in economia politica, bene di Giffen. Un bene di Giffen è un bene, una merce, essenziale, di base e di largo consumo, la cui domanda aumenta con l’aumentare del prezzo. La merce o prodotto di largo consumo costa di più ed essa è più richesta. Il suo prezzo aumenta ancora. Ancora più persone la domandano e la comprano, almeno in determinati contesti e sotto determinate condizioni. Tale tipo di comportamento, prima relegato alla teoria economica, è stato riscontrato, nelle ricerca citata (Jensen, July 2007), in Cina.
Robert Giffen (1837 – 1910), statistico ed economista, avrebbe formulato (secondo Alfred Marshall, che tuttavia non si sa bene dove abbia preso l’asserzione), la sua ipotesi relativamente a beni di largo consumo, sostenendo che se il prezzo del pane aumenta, restando esso il bene più economico, le famiglie a basso reddito ne acquistino perfino di più. Che ne acquistino di più in termini monetari è possibile o logicamente anche probabile, in taluni contesti. Che ne acquistino di più come quantità non è per nulla certo. Dipende comunque da altri fattori. Infatti, più pertinentemente, c’è chi parla o parlava di paradosso di Giffen, sperando che un un giorno se ne potesse trovare una qualche evidenza empirica che desse o al fascino intrinseco d’un pardosso o forse, più probabilmente, che fosse citato (poco importa se senza, o con occulta, precisione filologica), da un classico dell’economia tutt’ora correntemente insegnata, un qualche senso comprensibile a tutti. Ciò anche perché, da un punto di vista strettamente teorico, costruendo un caso con due beni di consumo, uno essenziale l’altro relativamente superfluo, se il prezzo del primo aumenta si può ottenere, sotto talune condizioni, che di esso se ne consumi di più anziché di meno. Si può dunque dimostrare teoricamente come il paradosso di Giffen possa verificarsi mentre non si può dimostrare teoricamente che esso sia una pura fantasia. Può essere provato come possibile, mentre non può essere dimostrato esso sia necessariamente o sempre falso.
Ora, sembra che sia stata trovata una qualche pertinenza al Giffen “citato” da Alfred Marshall. Le ricerca empirica sembra ben fondata e condotta, oltre che con costi per alterare comportamenti di consumo e dunque testarli.
“In an earlier (unpublished) version of this paper (Jensen and Miller 2002) using panel data from the China Health and Nutrition Survey, we found suggestive evidence that poor households in China exhibited Giffen behavior with respect to their primary dietary staple (rice in the south, wheat and/or noodles in the north). However, because the study relied on possibly endogenous variation in market prices, we were unable to identify a causal relationship between price changes and consumption. To address this concern, for the present study we conducted a field experiment in which for five months, randomly selected households were given vouchers that subsidized their purchases of their primary dietary staple. Building on the insights of our earlier analysis, we studied two provinces of China: Hunan in the south, where rice is the staple good, and Gansu in the north, where wheat is the staple.
“Using consumption surveys gathered before, during and after the subsidy was imposed, we find strong evidence that poor households in Hunan exhibit Giffen behavior with respect to rice. That is, lowering the price of rice via the experimental subsidy caused households to reduce their demand for rice, and removing the subsidy had the opposite effect. This finding is robust to a range of alternative specifications and methods of parsing the data. In Gansu, the evidence is somewhat weaker, and relies to a greater extent on segregating households that are poor from those that are too poor or not poor enough. We attribute the relative weakness of the case for Giffen behavior in Gansu to the partial failure of two of the basic conditions under which Giffen behavior is expected; namely that the staple good have limited substitution possibilities, and that households are not so poor that they consume only staple foods. Focusing our analysis on those whom the theory identifies as most likely to exhibit Giffen behavior, we find stronger evidence of its existence.”
Gli autori, come già la letteratura economica precedente, partono dall’assunzione che il consumatore povero sia guidato dalla necessità di assicurarsi un’adeguata assunzione di calorie. Creano dunque un modello con due merci di consumo alimentare, una di base ed una di piacere. A unità di spesa, le calorie date dalla merce di piacere (pur preferita per il gusto) sono inferiori a quelle dalla merce di base. Si possono immaginare carni da un lato e pasta o riso dall’altro. Sulla base di un vincolo di bilancio, il consumatore deve innanzitutto assumere le calorie necessarie alla propria sopravvivenza, poi, eventualmente, preoccuparsi della gradevolezza complessiva della propria alimentazione. Il consumatore di fronte alla presenza sul mercato di due merci delle caratteristiche dette, deve dunque massimizzare la propria funzione di sussistenza e la propria funzione di bilancio.
Nel testaggio empirico si deve sempre semplificare al massimo. In realtà, pur semplificando, non è vero che si creino necessariamente situazioni non realistiche. Se non si semplificasse, diverrebbe impossibile qualunque esperimento empirico oppure, nello sforzo di tenere conto di tutte le variabili, si creerebbero modelli ancora meno realistici. Provate a vivere di riso, o pasta, la merce di base, con condimenti vari (carni, vegetali relativamente costosi, etc.; la merce gradevole), tra l’altro il pasto di base nelle Cine, non solo per “poveri”, è proprio confenzionato così (quando non sia una sbobba liquida equivalente, a base di pasta più o meno galleggiante nel liquido, liquido che può essere più o meno ricco anche in termini di costo/prezzo), e vedrete che potete davvero vivere a quel modo e molti vivono a quel modo. In condizione di impoverimento (o impoverimento ulteriore) privilegerete il riso o pasta su ciò che lo rende gradevole o più gradevole.
Gli autori analizzano in dettaglio perché il comportamento di Giffen può riguardare, in concreto, solo un piccolo gruppo di consumatori.
“Poor Chinese consumers fit nicely with the assumptions of the model. The crucial feature leading to Giffen behavior is the presence of one predominant cheap source of calories, i.e., a single basic good. In our sample, the basic good is rice (in the south) or wheat (in the north), and the fancy good is pork and other meat. While other foods such as vegetables are consumed, they provide far fewer calories per yuan than staple grains, and therefore do not serve as basic goods; the intuition of the model easily extends to include foods such as this.”
Esistono, inoltre, altri vincoli analitici. Dunque, gli autori concentrano l’analisi empirica di conseguenza:
“A central problem in searching for Giffen behavior, and indeed in any analysis of demand, is finding both sufficient and exogenous price variation. As a practical problem, whether data are cross-sectional, time-series or panel, there is often not a great deal of variation in prices for the kinds of goods likely to be candidates for Giffen behavior. This applies especially to cross-sectional data, as arbitrage should eliminate spatial price differences, especially for easily storable and non-perishable commodities such as grains. And any remaining price variation may be due do unobservable quality differences. Beyond this, a more serious concern is that even with sufficient price variation, the source of that variation is often potentially endogenous, since price is the equilibrium of a system of simultaneous equations. A positive correlation between price and consumption could simply represent shocks to, or differences in, demand over space or time rather than Giffen behavior. Although instrumental variables could address this problem, finding instruments that shift supply but do not directly affect demand is difficult.
“To overcome these challenges, we conducted a field experiment in which we provided randomly selected poor households in two Chinese provinces with price subsidies for staple foods. In Hunan, a southern province, rice is the staple good, and in Gansu, a northwestern province, wheat is the staple good (consumed primarily as buns, a simple bread called mo or noodles). These regional ‘taste’ differences are primarily determined by geography, climate and history, with wheat the dominant crop grown in Gansu and rice dominant in Hunan. Accordingly, we subsidized rice (only) in Hunan and wheat flour (only) in Gansu.”
Per l’esperimento, sono stati creati tre gruppi di trattamento ed uno di controllo. Ai tre gruppi di trattamento sono stati dati buoni che permettevano sconti differenti per ognuno dei tre gruppi sul riso di base. In pratica, sono stati dati tre sussidi differenziati sul riso con accorgimenti e controlli per impedire che i buoni fossero oggetto di commercio, dunque usati per altri fini che lo sconto sul riso. È stato di conseguenza osservato in dettaglio il comportamento alimentare e di spesa degli individui dei vari gruppi. Si possono leggere i dettagli nel saggio sulla ricerca [(Jensen, July 2007)]. I risultati della regressione (econometrica) indicano le caratteristiche dei comportamenti.
“The theory predicts that only households that are poor, but not too poor, will exhibit Giffen behavior. Thus we would like to focus our study on households that are in the subsistence range, but not below it, or above it. Unfortunately, classifying households or individuals directly in this way is not possible. Not only is there no consensus on what constitutes a subsistence level of calories, but any such threshold would certainly vary widely by age, sex, height, weight, body fat and muscle composition, level of physical activity, health status and a range of other factors. As a result, although we can compute caloric intake for each individual, identifying whether specific individuals are below, near or above their subsistence level of caloric requirements is not possible. For the same reason, it isn’t possible to define these regions based on income or expenditure; individuals with different characteristics will require different amounts of expenditures or income to achieve nutritional sufficiency. Any such cut-offs would be imperfect, including some people who, because of high weight or activity levels, are unable to achieve maintenance nutrition with the specified income, and excluding others who have lower than expected nutritional (and thus income) needs because of small stature or low activity levels.
“The method of parsing the data we employ is based in the theory. Those who are so poor that they cannot achieve maintenance nutrition will consume a very high proportion of their food in the form of the staple good, regardless of size and activity level. Thus, splitting the data by the pre-intervention or initial share of caloric intake from consumption of the staple (initial staple calorie share, ISCS) provides a more direct measure of whether a consumer or household is welloff enough that they could, potentially, exhibit Giffen behavior. [...]”
Identificata l’area di potenziale estrinsecazione del comportamento di Giffen, gli autori procedono oltre nel testaggio del fenomeno.
“While the main goal of our study is to document Giffen behavior, we briefly explore a few implications of the subsistence model. We have already seen that consumers with very high staple calorie shares do not exhibit Giffen behavior. In addition, the model also predicts that once consumers are wealthy enough to pass beyond the subsistence zone into the standard consumption zone, staple demand should once again slope downward; in effect, we predict an ‘inverted-U’ shape, with downward sloping demand (negative coefficients) for low and high values of staple calorie share, and Giffen behavior (positive coefficients) for intermediate values. As stated, unlike the 80 percent calorie share, it isn’t possible to define a threshold beyond which households are likely to be in the standard or normal consumption zone, nor are we even certain our sample of the urban poor contains any such households. We therefore take a simple, flexible approach using a series of locally weighted regressions. [...]”
Ecco le conclusioni della ricerca come enunciate in (Jensen, July 2007):
“We find strong, clear evidence of Giffen behavior among poor households in Hunan, China, and somewhat less robust evidence in Gansu. To the best of our knowledge, this is the first rigorous empirical evidence of Giffen behavior. It is ironic that despite a long search, in sometimes unusual settings, we found examples in the most widely consumed foods for the most populous nation in the history of humanity. However, the examples were found exactly where theory would predict they should occur; impoverished consumers, heavily dependent on a staple good, with limited substitution possibilities.
“The results also underscore the vulnerability of extremely poor households to staple food price changes, and provide support for a view of very poor consumers as behaving as if they face a subsistence constraint and making consumption decisions in order to maintain nutritional sufficiency in the face of a changing environment. While consumers prefer to consume foods with non-nutritive attributes if they can afford them, they will trade-off these factors in order to maintain nutrition when the price of the staple food increases. However, while consumers behave in some ways as the subsistence model predicts, there remains important variation in tastes, as between those consuming the rice-based and wheat-based diets in China, that must also be taken into account. A complete understanding of the interaction between nutrition- and taste-based factors in poor consumers’ decision-making processes is beyond this scope of this paper but would have important implications for understanding the well-being and nutritional status of the poor, and would also have policy implications regarding food price subsidies or taxation.”
Jensen, R. T., and N. H. Miller, Giffen Behavior: Theory and Evidence, Working Paper 13243, NBER, Cambridge, MA, USA, July 2007,
http://papers.nber.org/papers/W13243
(Jensen, July 2007).
by Roberto Scaruffi
Jensen, R. T., and N. H. Miller, Giffen Behavior: Theory and Evidence, Working Paper 13243, NBER, Cambridge, MA, USA, July 2007,
http://papers.nber.org/papers/W13243
(Jensen, July 2007).
Robert T. Jensen
Nolan H. Miller
Il comportamento di Giffen è correntemente chiamano, in italiano, in economia politica, bene di Giffen. Un bene di Giffen è un bene, una merce, essenziale, di base e di largo consumo, la cui domanda aumenta con l’aumentare del prezzo. La merce o prodotto di largo consumo costa di più ed essa è più richesta. Il suo prezzo aumenta ancora. Ancora più persone la domandano e la comprano, almeno in determinati contesti e sotto determinate condizioni. Tale tipo di comportamento, prima relegato alla teoria economica, è stato riscontrato, nelle ricerca citata (Jensen, July 2007), in Cina.
Robert Giffen (1837 – 1910), statistico ed economista, avrebbe formulato (secondo Alfred Marshall, che tuttavia non si sa bene dove abbia preso l’asserzione), la sua ipotesi relativamente a beni di largo consumo, sostenendo che se il prezzo del pane aumenta, restando esso il bene più economico, le famiglie a basso reddito ne acquistino perfino di più. Che ne acquistino di più in termini monetari è possibile o logicamente anche probabile, in taluni contesti. Che ne acquistino di più come quantità non è per nulla certo. Dipende comunque da altri fattori. Infatti, più pertinentemente, c’è chi parla o parlava di paradosso di Giffen, sperando che un un giorno se ne potesse trovare una qualche evidenza empirica che desse o al fascino intrinseco d’un pardosso o forse, più probabilmente, che fosse citato (poco importa se senza, o con occulta, precisione filologica), da un classico dell’economia tutt’ora correntemente insegnata, un qualche senso comprensibile a tutti. Ciò anche perché, da un punto di vista strettamente teorico, costruendo un caso con due beni di consumo, uno essenziale l’altro relativamente superfluo, se il prezzo del primo aumenta si può ottenere, sotto talune condizioni, che di esso se ne consumi di più anziché di meno. Si può dunque dimostrare teoricamente come il paradosso di Giffen possa verificarsi mentre non si può dimostrare teoricamente che esso sia una pura fantasia. Può essere provato come possibile, mentre non può essere dimostrato esso sia necessariamente o sempre falso.
Ora, sembra che sia stata trovata una qualche pertinenza al Giffen “citato” da Alfred Marshall. Le ricerca empirica sembra ben fondata e condotta, oltre che con costi per alterare comportamenti di consumo e dunque testarli.
“In an earlier (unpublished) version of this paper (Jensen and Miller 2002) using panel data from the China Health and Nutrition Survey, we found suggestive evidence that poor households in China exhibited Giffen behavior with respect to their primary dietary staple (rice in the south, wheat and/or noodles in the north). However, because the study relied on possibly endogenous variation in market prices, we were unable to identify a causal relationship between price changes and consumption. To address this concern, for the present study we conducted a field experiment in which for five months, randomly selected households were given vouchers that subsidized their purchases of their primary dietary staple. Building on the insights of our earlier analysis, we studied two provinces of China: Hunan in the south, where rice is the staple good, and Gansu in the north, where wheat is the staple.
“Using consumption surveys gathered before, during and after the subsidy was imposed, we find strong evidence that poor households in Hunan exhibit Giffen behavior with respect to rice. That is, lowering the price of rice via the experimental subsidy caused households to reduce their demand for rice, and removing the subsidy had the opposite effect. This finding is robust to a range of alternative specifications and methods of parsing the data. In Gansu, the evidence is somewhat weaker, and relies to a greater extent on segregating households that are poor from those that are too poor or not poor enough. We attribute the relative weakness of the case for Giffen behavior in Gansu to the partial failure of two of the basic conditions under which Giffen behavior is expected; namely that the staple good have limited substitution possibilities, and that households are not so poor that they consume only staple foods. Focusing our analysis on those whom the theory identifies as most likely to exhibit Giffen behavior, we find stronger evidence of its existence.”
Gli autori, come già la letteratura economica precedente, partono dall’assunzione che il consumatore povero sia guidato dalla necessità di assicurarsi un’adeguata assunzione di calorie. Creano dunque un modello con due merci di consumo alimentare, una di base ed una di piacere. A unità di spesa, le calorie date dalla merce di piacere (pur preferita per il gusto) sono inferiori a quelle dalla merce di base. Si possono immaginare carni da un lato e pasta o riso dall’altro. Sulla base di un vincolo di bilancio, il consumatore deve innanzitutto assumere le calorie necessarie alla propria sopravvivenza, poi, eventualmente, preoccuparsi della gradevolezza complessiva della propria alimentazione. Il consumatore di fronte alla presenza sul mercato di due merci delle caratteristiche dette, deve dunque massimizzare la propria funzione di sussistenza e la propria funzione di bilancio.
Nel testaggio empirico si deve sempre semplificare al massimo. In realtà, pur semplificando, non è vero che si creino necessariamente situazioni non realistiche. Se non si semplificasse, diverrebbe impossibile qualunque esperimento empirico oppure, nello sforzo di tenere conto di tutte le variabili, si creerebbero modelli ancora meno realistici. Provate a vivere di riso, o pasta, la merce di base, con condimenti vari (carni, vegetali relativamente costosi, etc.; la merce gradevole), tra l’altro il pasto di base nelle Cine, non solo per “poveri”, è proprio confenzionato così (quando non sia una sbobba liquida equivalente, a base di pasta più o meno galleggiante nel liquido, liquido che può essere più o meno ricco anche in termini di costo/prezzo), e vedrete che potete davvero vivere a quel modo e molti vivono a quel modo. In condizione di impoverimento (o impoverimento ulteriore) privilegerete il riso o pasta su ciò che lo rende gradevole o più gradevole.
Gli autori analizzano in dettaglio perché il comportamento di Giffen può riguardare, in concreto, solo un piccolo gruppo di consumatori.
“Poor Chinese consumers fit nicely with the assumptions of the model. The crucial feature leading to Giffen behavior is the presence of one predominant cheap source of calories, i.e., a single basic good. In our sample, the basic good is rice (in the south) or wheat (in the north), and the fancy good is pork and other meat. While other foods such as vegetables are consumed, they provide far fewer calories per yuan than staple grains, and therefore do not serve as basic goods; the intuition of the model easily extends to include foods such as this.”
Esistono, inoltre, altri vincoli analitici. Dunque, gli autori concentrano l’analisi empirica di conseguenza:
“A central problem in searching for Giffen behavior, and indeed in any analysis of demand, is finding both sufficient and exogenous price variation. As a practical problem, whether data are cross-sectional, time-series or panel, there is often not a great deal of variation in prices for the kinds of goods likely to be candidates for Giffen behavior. This applies especially to cross-sectional data, as arbitrage should eliminate spatial price differences, especially for easily storable and non-perishable commodities such as grains. And any remaining price variation may be due do unobservable quality differences. Beyond this, a more serious concern is that even with sufficient price variation, the source of that variation is often potentially endogenous, since price is the equilibrium of a system of simultaneous equations. A positive correlation between price and consumption could simply represent shocks to, or differences in, demand over space or time rather than Giffen behavior. Although instrumental variables could address this problem, finding instruments that shift supply but do not directly affect demand is difficult.
“To overcome these challenges, we conducted a field experiment in which we provided randomly selected poor households in two Chinese provinces with price subsidies for staple foods. In Hunan, a southern province, rice is the staple good, and in Gansu, a northwestern province, wheat is the staple good (consumed primarily as buns, a simple bread called mo or noodles). These regional ‘taste’ differences are primarily determined by geography, climate and history, with wheat the dominant crop grown in Gansu and rice dominant in Hunan. Accordingly, we subsidized rice (only) in Hunan and wheat flour (only) in Gansu.”
Per l’esperimento, sono stati creati tre gruppi di trattamento ed uno di controllo. Ai tre gruppi di trattamento sono stati dati buoni che permettevano sconti differenti per ognuno dei tre gruppi sul riso di base. In pratica, sono stati dati tre sussidi differenziati sul riso con accorgimenti e controlli per impedire che i buoni fossero oggetto di commercio, dunque usati per altri fini che lo sconto sul riso. È stato di conseguenza osservato in dettaglio il comportamento alimentare e di spesa degli individui dei vari gruppi. Si possono leggere i dettagli nel saggio sulla ricerca [(Jensen, July 2007)]. I risultati della regressione (econometrica) indicano le caratteristiche dei comportamenti.
“The theory predicts that only households that are poor, but not too poor, will exhibit Giffen behavior. Thus we would like to focus our study on households that are in the subsistence range, but not below it, or above it. Unfortunately, classifying households or individuals directly in this way is not possible. Not only is there no consensus on what constitutes a subsistence level of calories, but any such threshold would certainly vary widely by age, sex, height, weight, body fat and muscle composition, level of physical activity, health status and a range of other factors. As a result, although we can compute caloric intake for each individual, identifying whether specific individuals are below, near or above their subsistence level of caloric requirements is not possible. For the same reason, it isn’t possible to define these regions based on income or expenditure; individuals with different characteristics will require different amounts of expenditures or income to achieve nutritional sufficiency. Any such cut-offs would be imperfect, including some people who, because of high weight or activity levels, are unable to achieve maintenance nutrition with the specified income, and excluding others who have lower than expected nutritional (and thus income) needs because of small stature or low activity levels.
“The method of parsing the data we employ is based in the theory. Those who are so poor that they cannot achieve maintenance nutrition will consume a very high proportion of their food in the form of the staple good, regardless of size and activity level. Thus, splitting the data by the pre-intervention or initial share of caloric intake from consumption of the staple (initial staple calorie share, ISCS) provides a more direct measure of whether a consumer or household is welloff enough that they could, potentially, exhibit Giffen behavior. [...]”
Identificata l’area di potenziale estrinsecazione del comportamento di Giffen, gli autori procedono oltre nel testaggio del fenomeno.
“While the main goal of our study is to document Giffen behavior, we briefly explore a few implications of the subsistence model. We have already seen that consumers with very high staple calorie shares do not exhibit Giffen behavior. In addition, the model also predicts that once consumers are wealthy enough to pass beyond the subsistence zone into the standard consumption zone, staple demand should once again slope downward; in effect, we predict an ‘inverted-U’ shape, with downward sloping demand (negative coefficients) for low and high values of staple calorie share, and Giffen behavior (positive coefficients) for intermediate values. As stated, unlike the 80 percent calorie share, it isn’t possible to define a threshold beyond which households are likely to be in the standard or normal consumption zone, nor are we even certain our sample of the urban poor contains any such households. We therefore take a simple, flexible approach using a series of locally weighted regressions. [...]”
Ecco le conclusioni della ricerca come enunciate in (Jensen, July 2007):
“We find strong, clear evidence of Giffen behavior among poor households in Hunan, China, and somewhat less robust evidence in Gansu. To the best of our knowledge, this is the first rigorous empirical evidence of Giffen behavior. It is ironic that despite a long search, in sometimes unusual settings, we found examples in the most widely consumed foods for the most populous nation in the history of humanity. However, the examples were found exactly where theory would predict they should occur; impoverished consumers, heavily dependent on a staple good, with limited substitution possibilities.
“The results also underscore the vulnerability of extremely poor households to staple food price changes, and provide support for a view of very poor consumers as behaving as if they face a subsistence constraint and making consumption decisions in order to maintain nutritional sufficiency in the face of a changing environment. While consumers prefer to consume foods with non-nutritive attributes if they can afford them, they will trade-off these factors in order to maintain nutrition when the price of the staple food increases. However, while consumers behave in some ways as the subsistence model predicts, there remains important variation in tastes, as between those consuming the rice-based and wheat-based diets in China, that must also be taken into account. A complete understanding of the interaction between nutrition- and taste-based factors in poor consumers’ decision-making processes is beyond this scope of this paper but would have important implications for understanding the well-being and nutritional status of the poor, and would also have policy implications regarding food price subsidies or taxation.”
Jensen, R. T., and N. H. Miller, Giffen Behavior: Theory and Evidence, Working Paper 13243, NBER, Cambridge, MA, USA, July 2007,
http://papers.nber.org/papers/W13243
(Jensen, July 2007).
