با همکاری انجمن اقتصاد کشاورزی ایران
نوع مقاله : مقالات پژوهشی
نویسنده
استادیار گروه اقتصاد کشاورزی، دانشکده کشاورزی، دانشگاه سید جمالالدین اسدآبادی. اسدآباد. ایران.
کلیدواژهها
عنوان مقاله English
نویسنده English
Introduction
Changes in food prices, shifts in purchasing power, and differences in household expenditure levels affect the consumption patterns of protein sources heterogeneously. In this context, understanding household demand responses to changes in expenditure and the prices of protein products is particularly important for assessing the welfare effects of price changes and designing effective food support policies. Given the substantial differences in households’ economic capacity, estimating demand elasticities at the aggregate population level may mask behavioral heterogeneity across expenditure groups. Therefore, this study aims to analyze the demand structure of the animal protein basket and examine differences in the responses of urban Iranian households across expenditure deciles.
Materials and Methods
The data used in this study were obtained from the Household Income and Expenditure Survey conducted by the Statistical Center of Iran and cover ten expenditure deciles of urban households over the period 1992–2024 (1371–1403 in the Iranian calendar). The animal protein basket considered in the analysis comprises red meat, poultry, fish, eggs, and dairy products. The dataset was organized as a balanced panel consisting of 330 observations, corresponding to ten expenditure deciles observed over 33 years. The price of each commodity group was calculated based on its unit value, defined as the ratio of expenditure to quantity consumed. To remove the effect of changes in the general price level, nominal values were deflated using the Consumer Price Index (CPI), with 2021 (1400) as the base year.
To estimate the demand system for the commodities under study, the Quadratic Almost Ideal Demand System (QUAIDS) was employed. Given the heterogeneity in household characteristics, household size and a dummy variable for the 2022–2024 period (1401–1403) were incorporated into the demand system using the demographic scaling approach proposed by Ray (1983) and its extension to the QUAIDS framework by Poi (2012). The demand system was estimated using the Seemingly Unrelated Regression–Iterated Nonlinear Least Squares (SUR-ITNL) method, subject to the theoretical restrictions of adding-up, homogeneity, and Slutsky symmetry. Subsequently, expenditure elasticities as well as Marshallian and Hicksian own- and cross-price elasticities were calculated and compared both for the full sample and across expenditure deciles.
Results and Discussion
The results of the Wald test indicated that the AIDS model is inadequate for explaining the demand pattern under investigation and that the quadratic term in the QUAIDS specification is statistically significant. This finding suggests that the relationship between household expenditure and demand for different protein groups among urban households in Iran is nonlinear, highlighting the necessity of employing the QUAIDS model to capture this behavioral pattern. The estimated expenditure elasticities for the full sample indicated that fish (1.524), red meat (1.115), and poultry (1.010) are classified as luxury goods, whereas dairy products (0.850) and eggs (0.478) fall into the category of necessity goods. However, the decile-specific analysis revealed that this aggregate classification masks an important degree of heterogeneity in consumption behavior. The expenditure elasticity of red meat declines from approximately 2.143 in the first decile to 0.819 in the tenth decile. Thus, red meat is a highly luxury good among lower-expenditure households but gradually approaches the status of a necessity good as expenditure increases. In contrast, the expenditure elasticity of poultry rises from 0.640 in the first decile to 1.359 in the tenth decile, indicating a transition from a necessity good at lower expenditure levels to a luxury good at higher expenditure levels. The expenditure elasticity of fish remains above unity across all expenditure deciles, whereas the expenditure elasticities of eggs and dairy products remain below unity throughout the distribution. The estimated Marshallian (uncompensated) price elasticities for the full sample show that all own-price elasticities are negative and consistent with the law of demand. In absolute terms, red meat (-1.307) and poultry (-1.205) exhibit the greatest price sensitivity, with elastic demand, whereas fish (-0.948), dairy products (-0.728), and particularly eggs (-0.363) exhibit inelastic demand. Price sensitivity is substantially greater among lower-expenditure households. For example, the absolute value of the Marshallian own-price elasticity of red meat declines from approximately 3.003 in the first decile to 0.889 in the tenth decile. For poultry, the corresponding magnitude decreases from approximately 1.711 to 1.037. Therefore, an increase in the prices of these commodities may lead to a substantially larger reduction in consumption quantities among households in the lower expenditure deciles. The Hicksian price elasticities reveal a similar pattern of heterogeneity. In the full sample, the Hicksian own-price elasticities for red meat, poultry, fish, eggs, and dairy products were -0.916, -0.976, -0.832, -0.324, and -0.502, respectively. The absolute value of the Hicksian own-price elasticity of red meat declines from 2.581 in the first decile to 0.553 in the tenth decile, while that of poultry decreases from 1.555 to 0.748. These findings indicate that the substitution effect associated with price changes is also stronger among lower-expenditure households, particularly for red meat and poultry. The analysis of Hicksian cross-price elasticities revealed significant substitution and complementarity relationships among different components of the animal protein basket. The most prominent substitution relationships were observed among red meat, poultry, and fish. Specifically, an increase in the price of red meat leads to an increase in the demand for poultry, with the intensity of this substitution being greater among lower-expenditure households. The elasticity of poultry demand with respect to the price of red meat declines from approximately 1.525 in the first decile to 0.215 in the tenth decile. In addition, the relationships among fish, eggs, and dairy products exhibit varying patterns of substitution and complementarity across some expenditure deciles, reflecting differences in the structure of household consumption baskets at different expenditure levels.
Suggestion
Overall, the findings demonstrate substantial heterogeneity in the demand for animal-source protein among urban households in Iran, with the magnitude of responses to expenditure and prices depending on both household expenditure levels and the type of protein commodity. Fish remains a luxury good across all expenditure deciles, whereas red meat follows a transition from a luxury good among lower-expenditure households toward a good closer to necessity status among higher-expenditure households. Conversely, poultry plays the role of a necessity good at lower expenditure levels but assumes a more luxury-oriented position at higher expenditure levels. Moreover, the greater price sensitivity of lower-expenditure households indicates that increases in the prices of major protein commodities may have more adverse consequences for these households. Accordingly, food-support policies should be targeted and tailored to expenditure deciles. In particular, strengthening the purchasing power of households in the lower expenditure deciles and facilitating their access to substitute sources of protein, alongside policies aimed at reducing the supply costs of commodities such as fish, may prove more effective than uniform policies applied across all households.
کلیدواژهها English
