Proving causal relationships using observational data

We describe a means of rejecting a null hypothesis concerning observed, but not deliberately manipulated, variables of the form H0: A -/-> B in favor of an alternative hypothesis HA: A --> B, even given the possibility of causally related unobserved variables. Rejection of such an H0 relies on the availability of two observed and appropriately related instrumental variables. While the researcher will have limited control over the confidence level in this test, simulation results suggest that type I errors occur with a probability of less than 0.15 (often substantially less) across a wide range of circumstances. The power of the test is limited if there are but few observations available and the strength of correspondence among the variables is weak. We demonstrate the method by testing a hypothesis with critically important policy implications relating to a possible cause of childhood malnourishment.causality, Monte Carlo, observational data, hypothesis testing, Research Methods/ Statistical Methods,

Rice World Market Prices

The marketing loan program associated with rice features benefits calculated using a USDA-announced World Market Price (WMP) rather than the posted county prices that are used for most other commodities. This results in reduced risk protection for producers relative to other crops, and greater difficulty in making optimal use of program benefits. This research investigates the rice WMP, identifying the relative importance of various foreign prices and other potential influencing factors. The results of this research have important implications for financial planning and optimal risk management strategies for rice producers.Agricultural and Food Policy,

Aggregate Milk Supply Response to the Milk Income Loss Contract Program

This research tests for changes in aggregate milk production due to the operation of the Milk Income Loss Contract (MILC) program since 2002. Aggregate production is decomposed into the size of the dairy herd and milk production per cow. We find no statistically significant response in either variable. This finding implies that the simultaneous operation of income and price support programs in the United States has not, thus far, proven self-defeating.dairy, income support, policy, price support, Agribusiness, Livestock Production/Industries,

Considerations in the Dairy Relocation Decision

Historically, U.S. dairymen have been thought to move to a new location to seek better economic opportunities or to leave an area that has become disadvantaged due to regulation or economics. Recently, there again have been major shifts in dairy production across the United States.Livestock Production/Industries,

The Net Effect of Exchange Rates on Agricultural Inputs and Outputs

For more than thirty years, studies about the effect of the exchange rate on exports have been conducted. However, few have considered the combined effect of the exchange rate on imported inputs into the agricultural system and the exports of final agricultural products those inputs produce. A current concern is for the net effect as the total value and quantity of inputs imported has increased. This research examines the effect of exchange rate changes on imported inputs into the corn, wheat, and beef cattle production systems. Effects on cost of production budgets are calculated, examining affects on profitability. Vector Autoregression (VAR) and Bayesian Averaging of Classical Estimates (BACE) models were estimated to evaluate those effects. Daily and weekly price data were used for corn, wheat, feeder steers, ethanol, diesel, ammonia, urea, di-ammonium phosphate, and the exchange rate. A VAR model was estimated to model the relationship between the variables. After having incongruous test results in determining the lag length structure it was decided that a BACE model would be approximated. After estimating the BACE model the price responses of the commodities to the exchange rates was estimated. The price responses were used in demonstrating the effect of the exchange rate on a producer’s profitability. It was determined that, generally, a strengthening exchange rate has a negative impact on prices. It was also found that the exchange rate has a greater impact on prices now than it did 14 years ago, implying that the exchange rate now has a greater affect on profitability. A one percent increase in the value of the dollar led to a decline in profitability ranging from $0.02/bu in wheat to$0.56/cwt in feeder steers. However, agricultural producers should not be overly concerned about a lower valued dollar from the perspective of their agricultural business.Agricultural and Food Policy, Crop Production/Industries, International Relations/Trade, Livestock Production/Industries,

Mold bolt and means for achieving close tolerances between bolts and bolt holes

In the space shuttle, a cargo bay storage rack was required which was to be manufactured from a metal-plastic composite and bolted to a cargo structure. Following completion, utilization of the rack was disallowed due to tolerances, that is, the size differences between the outside bolt diameter and the inside hole diameter. In addition to the space shuttle problem there are other close tolerance requirements for bolts. Such environments often benefit from close tolerance bolting. Frequently such fabrication is not cost effective. Consequently there is a need for means of achieving close tolerances between bolts and bolt holes. Such means are provided. After compressing the elements together a strong rigid plastic, ceramic, or ceramic plastic fluid is forced into a channel extending through the bolt

Educational Policy and Training Implications of Social Science Research: Lessons from an Inner City Elementary School

Participant observation research in an elementary school from 1989 to 1992 reinforces our understanding that often inner city children find a conflict between the behaviors and values that help them survive on the street and those that are expected in the middle-class educational system in which they are engaged on a day-to-day basis. While expecting middle-class responses, however, many teachers used archaic teaching strategies that have been abandoned in our best suburban schools. The research also makes clear the need for teachers to have high expectations for children while employing teaching methodologies that focus on individual students and their strengths and weaknesses. Policy recommendations are outlined that could alter the success of inner city education, if employed judiciously

Muscle force contributions to anterior cruciate ligament loading

Anterior cruciate ligament (ACL) injuries are one of the most common knee pathologies sustained during athletic participation and are characterised by long convalescence periods and associated financial burden. Muscles have the ability to increase or decrease the mechanical loads on the ACL, and thus are viable targets for preventative interventions. However, the relationship between muscle forces and ACL loading has been investigated by many different studies, often with differing methods and conclusions. Subsequently, this review aimed to summarise the evidence of the relationship between muscle force and ACL loading. A range of studies were found that investigated muscle and ACL loading during controlled knee flexion, as well as a range of weightbearing tasks such as walking, lunging, sidestep cutting, landing and jumping. The quadriceps and the gastrocnemius were found to increase load on the ACL by inducing anterior shear forces at the tibia, particularly when the knee is extended. The hamstrings and soleus appeared to unload the ACL by generating posterior tibial shear force; however, for the hamstrings, this effect was contingent on the knee being flexed greater than ~ 20° to 30°. The gluteus medius was consistently shown to oppose the knee valgus moment (thus unloading the ACL) to a magnitude greater than any other muscle. Very little evidence was found for other muscle groups with respect to their contribution to the loading or unloading of the ACL. It is recommended that interventions aiming to reduce the risk of ACL injury consider specifically targeting the function of the hamstrings, soleus and gluteus medius

Subject Retention in Prehospital Stroke Research Using a Telephone-Based Physician-Investigator Driven Enrollment Method.

Background and purposeSubject retention into clinical trials is vital, and prehospital enrollment may be associated with higher rates of subject withdrawal than more traditional methods of enrollment. We describe rates of subject retention in a prehospital trial of acute stroke therapy.MethodsAll subjects were enrolled into the NIH Field Administration of Stroke Therapy-Magnesium (FAST-MAG) phase 3 clinical trial. Paramedics screened eligible subjects and contacted the physician-investigator using a dedicated in-ambulance cellular phone. Physician-investigators obtained explicit informed consent from the subject or on-scene legally authorized representative (LAR) who reviewed and signed a consent form. Exception from informed consent (EFIC) was utilized in later stages of the study.ResultsThere were 1,700 subjects enrolled; 1,017 provided consent (60%), 662 were enrolled via LAR (39%), and 21 were enrolled via EFIC (1%). Of the 1,700 patients, 1,413 (83%) completed the 90-day visit, 265 (16%) died prior to the 90-day visit, and 22 (1.3%) withdrew from the study before completion. There were no differences in rates of withdrawal by method of study enrolment, i.e., self-consent (n = 14), 1.4%; LAR (n = 8), 1.2%; EFIC (n = 0) 0%.ConclusionThere was a high rate of retention when subjects were enrolled into prehospital stroke research using a phone-based method to obtain explicit consent