The formation of community based organizations in sub-Saharan Africa: An analysis of a quasi-experiment.

Previous analyses of the formation and comparison of community based organizations (CBOs) have used cross section data. So, causal inference has been compromised. We obviate this problem by using data from a quai-experiment in which villages were formed by government officials selecting and clustering households. Our findings are as follow: CBO co-memberships are more likely between geographically proximate households and less likely between early and late settlers, members of female headed households are not excluded, in poorer villages CBO co-membership networks are denser and, while wealthier households may have been instrumental in setting up CBOs, poorer households engage shortly afterwards.Community Based Organizations; quasi-experiment; social networks

An overview of inventory systems with several demand classes

In this chapter we discuss inventory systems where several demand classes may be distinguished. In particular, we focus on single-location inventory systems and we analyse the use of a so-called critical level policy. With this policy some inventory is reserved for high-priority demand. A number of practical examples where several demand classes naturally arise are presented, and the implications and modelling of the critical level policy in distribution systems are discussed. Finally, an overview of the literature on inventory systems with several demand classes is given

Who shares risk with whom under different enforcement mechanisms?

We investigate whether available enforcement mechanisms affects who shares risk with whom in sub-Saharan Africa by applying dyadic regression analysis to data from a lab-type experiment, surveys and a genealogical mapping exercise. During the experiment participants were invited to form risk sharing groups under three enforcement mechanisms: external, intrinsic, and extrinsic, i.e., social sanctioning. Dyads similar in age and gender or who belong to the same economic communitybased organizations (CBOs) are more likely to share risk. However, when social sanctioning is possible, co-members in economic CBOs withdraw from group formation and co-religion and marriage ties come to the fore.Barr, A. et al. (2010) Who shares risk with whom under different enforcement mechanisms? ESRC Working Paper, London: ESRC

Who shares risk with whom under different enforcement mechanisms?

We investigate whether available enforcement mechanisms affect who shares risk with whom in sub-Saharan Africa, by applying dyadic regression analysis to data from a lab-type experiment, surveys, and a genealogical-mapping exercise. During the experiment, participants were invited to form risk-sharing groups under three enforcement mechanisms: external, intrinsic, and extrinsic (i.e., social sanctioning). Same-sex dyads and dyads who belong to the same economic community-based organizations (CBOs) are more likely to share risk. However, when social sanctioning is possible, comembers in economic CBOs withdraw from group formation and coreligion, and marriage ties come to the fore

Inventory rationing in an (s, Q) inventory model with lost sales a two demand classes

Whenever demand for a single item can be categorized into classes of different priority, an inventory rationing policy should be considered. In this paper we analyse a continuous review (s,Q) model with lost sales and two demand classes. A so-called critical level policy is applied to ration the inventory among the two demand classes. With this policy, low--priority demand is rejected in anticipation of future high--priority demand whenever the inventory level is at or below a prespecified critical level. For Poisson demand and deterministic lead times, we present an exact formulation of the average inventory cost. A simple optimization procedure is presented, and in a numerical study we compare the optimal rationing policy with a policy where no distinction between the demand classes is made. The benefit of the rationing policy is investigated for various cases and the results show that significant cost reductions can be obtained

Bridging the gender divide: An experimental analysis of group formation in African villages

Assortative matching occurs in many social contexts. We experimentally investigate gender assorting in sub-Saharan villages. In the experiment, co-villagers could form groups to share winnings in a gamble choice game. The extent to which grouping arrangements were or could be enforced and, hence, the distribution of interaction costs were exogenously varied. Thus, we can distinguish between the effects of homophily and interaction costs on the extent of observed gender assorting. We find that interaction costs matter - there is less gender assorting when grouping depends on trust. In part, this is due to trust based on co-memberships in gender-mixed religions.

On the marginal cost approach in maintenance

In this paper we investigate the conditions under which the marginal cost approach of Refs. 1-3 holds. As observed in Ref. 4, the validity of the marginal cost approach gives rise to a useful framework of single-component maintenance optimization models, which covers almost all models used in practice. For the class of unimodal finite-valued marginal cost functions, we show that these optimization models are easy to solve

The break quantity rule in a 1-warehouse, N-retailers distribution system

In this paper the effect of the break quantity rule on the inventory costs in a 1-warehouse, N-retailers distribution system is analyzed. The break quantity rule is to deliver large orders from the warehouse, and small orders from the nearest retailer, where a so--called break quantity determines whether an order is small or large. Under the assumptions that the stock at the warehouse can only be used to satisfy large orders, and that demand during the leadtimes is normally distributed, an expression for the inventory costs is derived. The objective of this paper is to provide insight into the effect of the break quantity rule on the inventory holding costs, and therefore we present extensive computational results, showing that in many cases the rule leads to a significant cost reduction

On the newsboy model with a cutoff transaction size

In this paper we analyse the effect of satisfying in a different way customers with an order larger than a prespecified cutoff transaction size, in a simple newsboy setting. For compound Poisson demand with discrete order sizes, we show how to determine the expected costs and the optimal cutoff transaction size. Moreover, by approximating the distribution of the total demand during a period by the normal distribution one can determine an expression for the average cost function that depends on the cutoff transaction size only. A main advantage of this approximation is that the computational effort is much less. The quality of using the normal approximation is evaluated through a number of numerical experiments, which show that the approximative results are satisfactory

Effects of unilateral leg muscle fatigue on balance control in perturbed and unperturbed gait in healthy elderly

AbstractThis study assessed effects of unilateral leg muscle fatigue (ULMF) on balance control in gait during the stance and swing phases of the fatigued leg in healthy elderly, to test the assumption that leg muscle strength limits balance control during the stance-phase.Ten subjects (aged 63.4, SD 5.5 years) walked on a treadmill in 4 conditions: unperturbed unfatigued, unperturbed fatigued, perturbed unfatigued, and perturbed fatigued. The perturbations were lateral trunk pulls just before contralateral heel contact. ULMF was evoked by unilateral squat exercise until task failure. Isometric knee extension strength was measured to verify the presence of muscle fatigue. Between-stride standard deviations and Lyapunov exponents of trunk kinematics were used as indicators of balance control. Required perturbation force and the deviation of trunk kinematics from unperturbed gait were used to assess perturbation responses.Knee extension strength decreased considerably (17.3% SD 8.6%) as a result ULMF. ULMF did not affect steady-state gait balance. Less force was required to perturb subjects when the fatigued leg was in the stance-phase compared to the swing-phase. Subjects showed a faster return to the unperturbed gait pattern in the fatigued than in the unfatigued condition, after perturbations in swing and stance of the fatigued leg.The results of this study are not in line with the hypothesized effects of leg muscle fatigue on balance in gait. The healthy elderly subjects were able to cope with substantial ULMF during steady-state gait and demonstrated faster balance recovery after laterally directed mechanical perturbations in the fatigued than in the unfatigued condition