Copula Regression Spline Sample Selection Models: The R Package SemiParSampleSel

Sample selection models deal with the situation in which an outcome of interest is observed for a restricted non-randomly selected sample of the population. The estimation of these models is based on a binary equation, which describes the selection process, and an outcome equation, which is used to examine the substantive question of interest. Classic sample selection models assume a priori that continuous covariates have a linear or pre-specified non-linear relationship to the outcome, and that the distribution linking the two equations is bivariate normal. We introduce the R package SemiParSampleSel which implements copula regression spline sample selection models. The proposed implementation can deal with non-random sample selection, non-linear covariate-response relationships, and non-normal bivariate distributions between the model equations. We provide details of the model and algorithm and describe the implementation in SemiParSampleSel. The package is illustrated using simulated and real data examples

Copula regression spline models for binary outcomes

We introduce a framework for estimating the effect that a binary treatment has on a binary outcome in the presence of unobserved confounding. The methodology is applied to a case study which uses data from the Medical Expenditure Panel Survey and whose aim is to estimate the effect of private health insurance on health care utilization. Unobserved confounding arises when variables which are associated with both treatment and outcome are not available (in economics this issue is known as endogeneity). Also, treatment and outcome may exhibit a dependence which cannot be modeled using a linear measure of association, and observed confounders may have a non-linear impact on the treatment and outcome variables. The problem of unobserved confounding is addressed using a two-equation structural latent variable framework, where one equation essentially describes a binary outcome as a function of a binary treatment whereas the other equation determines whether the treatment is received. Non-linear dependence between treatment and outcome is dealt using copula functions, whereas covariate-response relationships are flexibly modeled using a spline approach. Related model fitting and inferential procedures are developed, and asymptotic arguments presented

A cause of ulnar neuropathy in a baseball pitcher

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66653/2/10.1177_036354658601400518.pd

Postoperative pulmonary edema in young, athletic adults

Pulmonary edema secondary to postextubation laryn gospasm is a potentially life-threatening problem, de manding early diagnosis and prompt treatment. We believe that this problem has been grossly underesti mated in its incidence, as only seven adults have been reported in the English literature, whereas seven adults have been observed at our institution in only a 24 month period. All were young, healthy, athletic adult males (average weight, 218 pounds) who underwent relatively minor, uncomplicated surgical procedures under gen eral anesthesia. Five of these patients were collegiate and/or profes sional athletes and had meticulous medical records detailing their clinical course. Clinical laryngospasm was noted immediately following extubation and anesthesia by mask with subsequent pulmonary edema. The di agnoses were confirmed by clinical examination, arterial blood gas determinations or pulse oximetry, and chest roentgenogram. Four adults required reintubation. Six of the seven adults demonstrated very rapid resolution of the pulmonary edema with prompt diagnosis and institution of a therapeutic regimen including oxygen, diuretics, reintubation, and/or positive pressure venti lation. In one patient, the problem was not immediately recognized, and progressed to florid pulmonary edema requiring emergent intubation 14 hours later in the emergency room, and 3 days of mechanical ventilation. The etiology of pulmonary edema following upper airway obstruction represents an interplay between several factors: cardiogenic and neurogenic mecha nisms, as well as hypoxia contribute. In this group, excessive negative intrathoracic pressure generated by forced inspiration against a closed glottis is the most likely, consistent, and logical explanation. This study suggests that young, healthy, athletic males may be at increased risk for this complication. We believe that their enhanced ability to generate ex cessive negative intrathoracic pressures is, at least in part, responsible. A heightened awareness of the prob lem in this at-risk group should invoke special consid erations, including choice of anesthesia, precautions on extubation, prolonged monitoring in the recovery phase if laryngospasm is observed or suspected, and rapid therapeutic intervention.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66519/2/10.1177_036354659101900407.pd

Applying Lean Techniques to Improve the Patient Scheduling Process

A patient's access to healthcare resources often begins with scheduling an appointment with a medical doctor or other provider. An inefficient scheduling system leads to unnecessary delays in providing care for patients and frustration for referring physicians. We used the tools of lean thinking to evaluate our current scheduling system, remove wasteful processes and procedures, and implement a more efficient and effective system. In doing so, we increased the value for our patients, who benefit from more timely access to care and greater satisfaction.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73944/1/j.1945-1474.2009.00025.x.pd

The Effect of Exercise, Prewrap, and Athletic Tape on the Maximal Active and Passive Ankle Resistance to Ankle Inversion

This investigation explored alternatives to the null hy potheses that maximal active and passive resistance to inversion developed by a near-maximally inverted and weightbearing ankle is not altered by 1) the use of prophylactic adhesive athletic tape, 2) the use of non- adhesive prewrap (underwrap), or 3) 40 minutes of vigorous exercise. Ten healthy men and 10 healthy women (mean age, 25 ± 3 years) with no recent ankle injuries underwent testing to determine maximal ankle resistance to inversion under unipedal, weightbearing conditions. Tests were performed with and without the support of athletic tape, and before and after 40 min utes of exercise. Half the testing sessions were per formed with prewrap under the tape. At 15° of inver sion, without any external ankle support, healthy young men and women could maximally resist a mean (SD) inversion moment of 52.9 (6.4) N-m and 28.3 (5.8) N-m, respectively. Although use of ankle tape provided a 10% increase in maximal resistance to inversion moments, this increase diminished to insignificant lev els after 40 minutes of vigorous exercise. Use of pre wrap improved maximal resistance to inversion by more than 10%.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66568/2/10.1177_036354659702500203.pd

Quantitative analysis of the measuring capabilities of the KT-1000 knee ligament arthrometer

The KT-1000 arthrometer was evaluated in vitro and in vivo to determine accuracy and quantify effects of potential error sources in clinical application. The KT- 1000 arthrometer in vitro accuracy was evaluated by making 30 measurements of 13 known displacements (range, +15 to -15 mm). The effect of applied force on malalignment measurements was evaluated in vitro by making repeated measurements with force applied 5°, 10°, and 15° from the vertical position. The effect of malpositioning the device along the joint line was eval uated in vivo by making repeated measurements 1 cm proximal and 1 cm distal to the joint line. The KT-1000 arthrometer was accurate in vitro (average error, 0.13 mm; SD, 0.12 mm). The range of measurements in creased when the angle of force application was in creased. Positioning the device 1 cm proximal to the joint line produced larger anterior translation measure ments in vivo than those at the joint line (5.8 versus 5.4 mm), while positioning it 1 cm distal produced smaller measurements (4.4 mm). The KT-1000 arthrometer's accuracy indicates great potential for clinical applica tion, but one must ensure that the displacing force is directed properly and the device is positioned accu rately over the joint line.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66953/2/10.1177_036354659302100520.pd

Arthroscopic meniscal repair evaluated by second-look arthroscopy

Of 353 arthroscopic peripheral meniscal repairs per formed using the "outside to inside" suturing technique with rasp preparation of the tear region, 74 repairs (50 medial and 24 lateral) were assessed by second-look arthroscopy and are the basis of this report. Results were graded as either healed, incompletely healed, or failed; these findings were correlated with clinical symp toms and associated ACL deficiency. Overall, asymp tomatic healing occurred in 84%, with 65% healed and 19% incompletely healed. The failure rate was 16%. All failures were symptomatic while all healed and incom pletely healed menisci were asymptomatic. Failure was associated with ACL deficiency in all cases. No failures occurred in either an ACL uninjured knee or an ACL reconstructed knee. Failure was also associated with tear location in the posterior horn of the medial menis cus. Eleven of 12 failures (92%) involved posterior medial meniscal tears with only 1 failure located pos terolaterally. Visual evidence of healing required a 4 month time interval.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68119/2/10.1177_036354659101900614.pd