Introduction

Market liberalization and trade liberalization in Mexico late last century, laid the foundation for the emergence of a competitive economy on the international market (^{De la Madrid, 1983}; ^{Salinas, 1989}). As free market economy, prices are set by the marginal cost of the most inefficient company involved, so those who cannot be part, have to change to another market, or disappear as a company, (^{Nicholson, 2005}). This means that companies have to be winners and losers, sectors also winners and losers. This caused displacement of labor and unemployment, when the sectors concerned not absorbed labor from the losers (^{Avila et al., 2008}).

In the agricultural sector market liberalization and trade liberalization, only benefited large specialized producers, while the losers were in the small and medium producers; producers who have been, have responded by increasing production and yields to compensate for the decline in prices, the value of their production, and their income (Puyana and Romero, 2008); however, this response has not been widespread, and some of the producers and agricultural workers have emigrated to other sectors of the economy or abroad (^{López et al., 2011}; ^{Eliosa-Martínez, 2012}) in relative terms the population employed in the agricultural sector has ebbed and occupied in the industrial sector and service (^{Cortez et al., 2008}).

The source of income is a critical variable, from the economic point of view, the decisions of the head of the family to stay or not in its production unit. For example, small producers in three micro regions of the municipality of Oxchuc, Chiapas, due to their low yields, families supplement their income by planting cash crops and the provision of services (^{Roman and Hernandez, 2010}). This income, in cash or in kind, should be enough for the family to meet their needs to which they are accustomed. When not reached, the head of the family tends to change its portfolio of income and undertakes new activities or deepens in others. On this point, ^{Guzman, et al. (2005)} found in Tepeji del Rio Hidalgo Mexico that rural income is no longer equivalent to farm income and rural families increasingly incorporate activities other than agriculture, as a way to compensate for low farm incomes. This income is formed from internal sources: the work of the head of the family, the couple, and the other members of the family nucleus (^{Yúnez and Naude, 2001}; ^{Lozano, 2003}), and external and government or private subsidies. The work of the household head is developed in its production unit and beyond. Within its production unit behaves as a producer and can sometimes have employees, while outside it generally behaves as a wage earner in the labor market. To the extent that the head of household increases time employment in the labor market, lowers dedicated to its production unit. When this is the case, the production unit becomes directed generally by the couple, a family, rented, or in the worst case, abandoned.

In the marginal zone of the state of Campeche, which includes urban and rural producers who produce agricultural products or other, and are characterized by low income, live more than 210 thousand habitants which represent about 30% of the population entity (^{INEGI, 2010}).

Given the agronomic and socioeconomic conditions of the state of Campeche, particularly the most marginalized area, agriculture that develops it is not competitive, among other reasons, because of the poor soil, the production system temporary lack of capital, technology among others; which result in low yields, poor quality agricultural products, and the difficulty of marketing them benefits the producer (^{Pat, 2010}). In the city, small businesses often require other lines of work have to support themselves, to the ravages of companies have increased productivity and become more competitive. Both small (agricultural or not) producers need to diversify their incomes, for which see the need to supplement them with others obtained outside their production units. When this is the case, alternatives to get a good salary depends on several factors, including, socioeconomic are of interest to this study. Hence the objective to evaluate the importance of some socioeconomic variables, especially income in the decision of the head of marginalized family of Campeche, to stay or not in its production unit.

Results and discussion

According to the model set out above for the case of Logit for individual data was: Li= -1.6206 + 0.0274 gender + 0.0549 age + 0.0748 Esc - 0.00004 IngMon. As shown in Table 1.

Table 1 Results of regression to the state of Campeche processed data. Logit model. 

Número de obs = 140 LR Chi2(4)= 22.55 Prob > chi2 = 0.0002 Log likelihood= -162.165; McFadden R-Squared= 0.122101 *Significativa; Fuente: Elaboración propia con base en muestra obtenida del ENIGH 2010 y resultados del paquete SAS y GRETL.

The estimators of the model parameters are not marginal effects on both these models depend on the values taken by the explanatory variables. They can, therefore, be calculated marginal effects for each observation of the sample, obtaining the mean effects average of the individual effects. Alternatively, the marginal effects can be evaluated for the mean value of the explanatory variables. For large sample sizes, test the null hypothesis is accepted or rejected is based on the Wald statistic, which has a chi-square distribution. According to Table 1 the coefficients of the variables that are significant, different from zero, for a significance level of 0.05, plus the intercept, are age and monetary income. The regressor variables that had an impact on the exogenous variable were old and monetary income, while gender and schooling were not significant, according to the statistical likelihood ratio (RV) equal to 22.55 whose probability value was 0.0001 which is small and meaningful.

It is worth mentioning that in models with binary returned, the goodness of fit is not very important, are included for illustrative purposes only. What really matters are the expected signs of the regression coefficients and their practical importance and statistics. For the pseudo square R model used was the R square McFadden who was 0.1221.

The calculated equation Logit is used to obtain the probability that the income of the production unit are higher than those obtained outside it; applying this to a householder of male, with an average age of 56 years with an educational level of fourth grade, and average income of 20,488 pesos, the probability that the income of the production unit is greater than you would get out, is about 29%, suggesting that, with these characteristics, the producer would be encouraged to neglect its production unit. The size of family income acts negatively. As it increases, decreases the chances of that generated in the production unitis greater than you get out. This suggests that increases in household income are positively correlated with the increase in employment outside the production unit. This strategy can continue, while the expectations of the household head working out are preferable (^{Huffman, 1980}).

The alternative of head of household employed outside the production unit is a frequent activity and corresponds to the strategy that has the head of the family to adapt to changes that occur in their levels of income and expense (^{Taylor et al., 1999}). The income obtained by employed outside the production unit serves as a complement to that obtained inside. The problem that can be generated, is that the roles are reversed, and the supplementary income becomes the more important because the odds that the production unit becomes secondary activity increase, is rented, or abandoned (Contreras et al., 1992).

It is common to find householders in the elderly; however, they are not elderly, since the average is between 51 years. Age acts positively to revenue production unit tend to be higher than those obtained outside. It means that there is a tendency that the production units, agricultural or not, characterized by generating most of household expenditure, the activities are in the hands of householders elderly. This strategy allows the accumulated experiences over time can be used to better manage the production unit; however often in these units the income generated is laconic, householders in elderly are responsible for these activities because they have no alternative, and because their descendants migrate and send remittances to families (^{Taylor et al., 1999}; ^{Mora, 2004}).

The schooling of heads of household is poor, on average did not finish primary in all deciles (Table 2). This variable is not significant in the model; however, in other studies (^{Huffman, 1980}; ^{Taylor, 2000}) the importance of it in the form that affects the choices of families on the activities from which they derive income plus that this variable significantly related to rural home stands new sources of revenue including the work of migrants. The authors find that education has high yield income households, both in their agricultural activities and non-agricultural. They also find that, as education increases, the returns to education move to other than those related to crop production activities. These results indicate the wealth of taking into account the schooling variable, and analyze the conditions which must be included, because it seems to be an important element to explain the family income.

Table 2 Characteristics of heads of households by income levels. Deciles. Simple averages. 

Fuente: Datos elaborados en base a la muestra extraída de la ENIGH, 2010

The gender variable is not significant in the models, and except for some deciles (Table 2), seems to be generalized to men who are heads of households trend. According to the model, if the household head is male or female, no influence to explain why household income is greater in the production unit outside.

Conclusions

Over time has been normal for marginal producers (agricultural or not), supplement their expenses with income from work performed outside their production unit, as traditional strategy to changes in income, prices and wages that are presented in their environment. However, this study indicates that increased household income from marginal producer in the state of Campeche, is positively correlated with the income earned outside their production unit, so it could be a weight ratio of the gradual change of activity master of the household head, relegating the original to a secondary activity, renting its production unit, or even deserting.

Work also indicates that the age of the household head positively acts to revenue production unit are greater than those obtained outside. Since these householders are not elderly, on average, you can use this feature to the new momentum of its original activities, supporting avoid migrating to these householders to illusory poles of development where they are integrated as unemployed, underemployed and with minimum social benefits. The financial support from the rest of the family and well- targeted government subsidies, can play a major role in this strategy.

There is empirical evidence that schooling of the household head, helps explain the source of income, so it should still be considered in these models.