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The matched group analysis method in prospective studies is a variation of matched pairs analysis with the advantage of sampling error avoided in the choosing of pairs of subjects. An example is shown in which comparisons are given of mortality in triads of cases classified by the tar and nicotine level of the cigarettes they smoked and matched on 10 variables. The method can also be used in retrospective and autopsy studies.
We report the results of a nonrandomized, matched group survival study comparing 29 patients with a choroidal or ciliary body melanoma managed by enucleation alone to 29 patients managed by enucleation following external beam ocular irradiation (20 Gy in five fractions over 5-7 days just prior to enucleation). Variables on which the patients in the two groups were matched included age at time of enucleation, largest linear tumor dimension, location of the anterior tumor margin relative to the equator and ora serrata, melanoma cell type, and extrascleral tumor extension. The cumulative 5-year survival in the enucleation alone group was 57.9% (SE = 9.9%), whereas that in the preenucleation radiation therapy group was 63.9% (SE = 12.2%). This difference is not statistically significant (p greater than 0.5, Mantel-Haenszel test). The authors discuss the strengths and limitations of their study and the implications of their results.
Group-matching designs are commonly used to identify the diagnosis-specific characteristics of children with developmental disabilities. In this paper, we address three issues central to the use of this design. The first concerns the alpha level to be used for considering groups to be matched on the control variable(s). The second involves the measurement characteristics of the control and target variables. We discuss the properties of standard scores, raw scores, and age equivalents and argue against the use of age equivalents. In addition, we consider the appropriateness of the commonly made prediction that groups that are matched for a control variable such as language ability or nonverbal reasoning ability but are not matched for chronological age should perform at equivalent levels on the target variable. Finally, we discuss issues related to the interpretation of significant between-group differences on the target variable, assuming groups are well-matched on the control variables, and describe the benefits of a method that focuses on characterizing a disorder on a case-by-case basis and then aggregating the cases, using the measures of sensitivity and specificity from signal detection theory.
Osteolysis and component loosening secondary to polyethylene (PE) debris are of paramount concern to today's joint replacement surgeon. This retrospective clinical study measures linear wear in 568 implanted total hip prostheses in which three different metals were used as bearing surfaces (307 stainless steel T-28 [Zimmer, Warsaw, IN], 162 cobalt chrome Tr-28 [Zimmer], and 99 nonion implanted titanium Miami Orthopedic Surgical Consultants [Biomet, Warsaw, IN] prostheses) implanted by a single surgeon over an 8-year period. The acetabular component in all cases was nonmetal-backed compression-molded PE, and all components were cemented. Linear wear was measured using the radiographic technique described by Livermore et al. (The effect of femoral head size on wear of the polyethylene acetabular component. J Bone Joint Surg 72A:518, 1990) in which change in acetabular component thickness is determined from serial radiographs. A separate evaluation of this technique confirmed accuracy to within 0.18 mm. Radiographs were also evaluated for femoral and acetabular radiolucencies, femoral subsidence, and osteolysis. Patients were matched for sex, age, weight, and length of follow-up period to eliminate these retrospective variables for comparison of wear. The patient-matched groups consisted of 77 patients from each group (43 women, 34 men) with the following demographics: age, 66 years; weight, 158.9 lbs.; follow-up period, 7.9 years. Results revealed linear wear rates of 0.06 stainless steel, 0.05 cobalt chrome, and 0.08 titanium in the patient-matched groups.(ABSTRACT TRUNCATED AT 250 WORDS)
Motorcyclists and a matched group of non-motorcycling car drivers were assessed on behavioral measures known to relate to accident involvement. Using a range of laboratory measures, we found that motorcyclists chose faster speeds than the car drivers, overtook more, and pulled into smaller gaps in traffic, though they did not travel any closer to the vehicle in front. The speed and following distance findings were replicated by two further studies involving unobtrusive roadside observation. We suggest that the increased risk-taking behavior of motorcyclists was only likely to account for a small proportion of the difference in accident risk between motorcyclists and car drivers. A second group of motorcyclists was asked to complete the simulator tests as if driving a car. They did not differ from the non-motorcycling car drivers on the risk-taking measures but were better at hazard perception. There were also no differences for sensation seeking, mild social deviance, and attitudes to riding/driving, indicating that the risk-taking tendencies of motorcyclists did not transfer beyond motorcycling, while their hazard perception skill did.
The results of 73 total knee arthroplasties in 67 patients after a high tibial osteotomy (HTO) were carefully reviewed at an average follow-up period of 73 months (range, 24-132 months). An extensive clinical as well as radiographic review was performed in an attempt to evaluate parameters that might portend more favorable or worse outcomes. Additional comparisons were made with two groups of 73 primary TKAs matched according to age, gender, diagnosis, prosthetic fixation, and length of follow-up period. The two comparison groups differed in that one (Group A) was additionally matched to deformity before TKA with a second comparison group (B) matched to pre-HTO deformity. On the basis of a 100-point knee rating scale, 36% of the study group patients had either a fair or poor result or required additional surgery. This was significantly greater than either comparison group (p < 0.01). Factors that prognosticated a worse outcome in the HTO patients (p < 0.01) included (1) workmen's compensation patient, (2) history of reflex sympathetic dystrophy after HTO, (3) early onset (less than one year) or no period of relief of pain after HTO, (4) multiple surgeries before HTO, and (5) an occupation as a laborer.
We report the results of a nonrandomized, matched-group, survival and visual preservation study of patients with a choroidal or ciliary body melanoma managed by microsurgical resection of the tumor versus cobalt-60 episcleral plaque radiotherapy. Each treatment group consisted of 30 patients. All patients were matched on a case-by-case basis in terms of tumor size (largest linear tumor dimension), location of the anterior tumor margin relative to the ora serrata, location of the posterior tumor margin relative to the equator, and age at the time of treatment. Although the estimated actuarial 5-year survival probability was slightly greater in the resection group (85.2%) than in the cobalt plaque group (81.8%), this difference was neither clinically impressive nor statistically significant. In contrast, there was a substantially higher rate of early posttreatment severe visual loss in the resection group (P = .0008, Mantel-Haenszel test).
Visual evoked cortical potentials (VECPs) to midperipheral stimulation of the visual field were elicited in age-matched groups of patients with unilateral chronic simple glaucoma or ocular hypertension and normal subjects. With a multimodal stimulus approach comprising transient and steady-state pattern reversal and transient onset-offset VECPs, 82.1% of the glaucoma group and 50.9% of the ocular hypertensives revealed significant abnormalities (p less than 0.01) in one or more of the electrophysiological features measured, i.e., latency, phase, amplitude, and contrast threshold.
The treatment process with two prototypic neuroleptics--haloperidol and chlorpromazine--and the nontherapeutic effects of trihexyphenidyl on this process were studied in carefully matched groups of ten schizophrenics each, using a "double-blind", repeated-measure, longitudinal research design. Measurements of various aspects of psychopathology, social participation and clinical indices of arousal were made periodically and objective test of cognition and attention were given. The two treatment groups were highly comparable in epidemiological and clinical terms and differed significantly during the baseline period in only one of the 39 parameters. Longitudinal nonparametric analyses showed that significant therepeutic changes tended to occur more quickly and involved a wider spectrum of schizophrenic phenomena with haloperidol than with chlorpromazine. Parametric analyses also indicated that at the completion of the study, haloperidol-treated patients had significant improvement in many more dimensions than the chlorpromazine-treated patients and that the changes with haloperidol were generally of greater magnitude. At the same time, chlorpromazine treatment seemed to be more susceptible to the antagonistic effects of trihexyphenidyl. No differential patterns of responses were noted for the two neuroleptics to provide any clinical validity to the distinction often made between "sedative" and "activating" neuroleptics. These data were in agreement with those from a previous comparative study which had a very different research design and a somewhat different type of schizophrenic population. The clinical and potency differences between the two neuroleptics were again explained on the basis of the fact that chlorpromazine has much stronger built-in anticholinergic properties, which may be acting in opposition to the antipsychotic activity. It was suggested that the degree of inherent anticholinergic activity may be an important determinant of potency differences among presently known neuroleptics. The possible role of cholinergic mechanisms in schizophrenia was discussed.
BACKGROUND: Recently the United Network for Organ Sharing (UNOS) began a pilot study to evaluate prospectively the merits of an allocation of cadaveric kidneys based on broader classes of HLA antigens, called cross-reactive groups (CREG). The objectives of the pilot study consider patient outcomes, but not the potential economic impact of a CREG-based allocation. This study predicts the impact of a CREG-based local allocation of cadaveric kidneys on 3-year Medicare payments and graft survival. METHODS: The UNOS renal transplant registry was merged to Medicare claims data for 1991-1997 by the United States Renal Data System. Average accumulated Medicare payments and graft survival up to 3 years posttransplant for first cadaveric renal transplant recipients were stratified by cross-reactive group mismatch categories. The economic impact was defined as the difference in average 3-year costs per transplant between the current and proposed allocation algorithms. Average 3-year costs were computed as a weighted average of costs, where the weights were the actual and predicted distributions of transplants across cross-reactive group categories. RESULTS: Results suggest that an organ allocation based on cross-reactive group matching criteria would result in a 3-year cost savings of $1,231 (2%) per transplant, and an average 3-year graft survival improvement of 0.6%. CONCLUSIONS: Cost savings and graft survival improvements can be expected if CREG criteria were to replace current criteria in the current allocation policy for cadaveric kidneys, although the savings appear to be smaller than may be achievable through expanded HLA matching.
PURPOSE: Currently no randomized studies show the relative morbidity and mortality of the open and endoluminal methods of abdominal aortic aneurysm (AAA) repair. The aim of this study was to analyze the outcome of two matched groups of patients with AAA, one undergoing open repair and the other undergoing endoluminal repair. METHODS: Two groups of patients who had undergone repair of AAA by open technique (group 1) or by endoluminal methods (group 2) were compared. A historic control cohort of 27 patients was selected from 56 consecutive patients who underwent open repair of AAA between January 1991 and February 1992. Patients considered unsuitable for the endoluminal method on the basis of computed tomography and aortography were excluded (n=29). Between May 1992 and November 1994 prospective data were recorded for 62 consecutive patients who underwent endoluminal repair by tube or bifurcated endografts. Twenty-eight patients who had been specifically referred for endoluminal AAA repairs because of preexisting severe medical comorbidities were excluded. Six of the endoluminal cases had failure, requiring conversion to open operation, and were excluded for separate analysis, leaving 28 patients in group 2. Patients in both groups were thus fit and suitable for either open or endoluminal repair and were comparable in relation to age, sex, risk factors, dimensions, and form of AAA. RESULTS: The mean values for operation time, blood loss, intensive care stay, and hospital stay for group 1 and group 2 were 2.6 versus 3.1 hours, 1422 versus 873 ml,* 1.8 versus 0.7 days,* and 12.4 versus 11.1 days, respectively (*p<0.05). Local/vascular complications occurred in 15% of patients in group 1 compared with 25% in group 2 (p=0.55), whereas remote/systemic complications occurred in 37% and 29%, respectively (p=0.3). Five of 28 patients in the endoluminal group had complications requiring early operative repair (n=3) or late revision (n=2). When comparison was made on an intention-to-treat basis (with failed procedures included), the incidence of local/vascular complications was significantly greater for endoluminal repair (p=0.047). CONCLUSIONS: The incidence of systemic/remote complications was similar for the two groups in spite of significantly less blood loss and shorter intensive care unit stay with endoluminal repair. The incidence of local/vascular complications had a tendency to be higher for endoluminal compared with standard open method (and was significantly greater if failed procedures were included). In this early experience with prototype devices, patients who were medically suitable for open surgical procedures did not derive benefit from the less invasive endoluminal technique with respect to duration of operation, length of hospital stay, or perioperative morbidity and mortality. On the other hand, because they also did not have worse outcome, a randomized study is now justified in this group.
Although patellofemoral symptoms after patellar-retaining knee arthroplasty are common, no evidence has been published in the literature on the potential benefit from patellar resurfacing at a later stage. This study evaluates the effect of secondary (delayed) patellar resurfacing using comparisons between 2 case-matched groups of patients with primary and secondary patellar resurfacing. Furthermore, multivariate statistical methods were applied to study factors that may influence the final outcome. Our results suggest that although significant clinical improvement was seen after delayed patella resurfacing, the outcome of secondary patellar resurfacing is inferior to that expected for a similar group of patients with primary resurfacing. Furthermore, the timing (delay period) of the secondary resurfacing procedure appears to negatively affect the final outcome. This suggests that secondary patellar resurfacing, when indicated, should be considered at an early stage.
This paper compares attention deficit disorder (ADD) with hyperactivity (ADDH) and without hyperactivity (ADDWO). The literature is outlined, revealing the areas of possible differences to be not only the core symptoms, but also associated conduct and emotional symptoms, social relations functioning, learning, medical disorders, family history, and course and outcome of the disorder. Empirical data are presented comparing age and sex matched groups of children from a speech/language clinic sample with ADDH (N = 40) and ADDWO (N = 40). Although the methods of the present study are different from those of previous studies, they nonetheless support a number of previous findings, and, further, give support to the external validity of the ADDWO diagnostic category.
We compared brain activation patterns between musicians and non-musicians (matched in performance score) while they performed a pitch memory task (using a sparse temporal sampling fMRI method). Both groups showed bilateral activation of the superior temporal, supramarginal, posterior middle and inferior frontal gyrus, and superior parietal lobe. Musicians showed more right temporal and supramarginal gyrus activation while non-musicians had more right primary and left secondary auditory cortex activation. Since both groups' performance were matched, these results probably indicate processing differences between groups that are possibly related to musical training. Non-musicians rely more on brain regions important for pitch discrimination while musicians prefer to use brain regions specialized in short-term memory and recall to perform well in this pitch memory task.
A young (X = 36.8 years) and an old (X = 52.9 years) group (n = 12) matched for physical fitness performed a graded exercise test at the beginning and after a 4-month physical fitness program consisting of calisthenics, jogging, and recreational activities. The purpose of the study was to determine if there were any differences in response to physical training in the two age groups of similar fitness. Sixteen physiological and four biochemical variables were measured. There was no significant difference in VO2 max between the young and old groups. Also, there were no significant differences between groups for serum total lipids, cholesterol, triglycerides, or glucose levels. The effects of the training program were similar for both the young and old groups.
An investigation, using a prospective cohort study, was performed to estimate the prolongation of hospital stay caused by nosocomial infections in surgical patients. An evaluation of the one-to-one matching method, as a model for similar studies was also undertaken. Between 1992 and 1994, 225 of 1482 surgical patients (15%) developed infection. Of these, 223 evaluable patients were compared with 1256 uninfected cases, in an unmatched analysis. In a further analysis, 151 infected cases were matched one-to-one with uninfected controls, and other factors such as age, length of preoperative stay, presence of malignancy or diabetes and presence of foley catheters or drains, were evaluated. Patients with infection were hospitalized for 10.6 days longer than the matched controls. In the unmatched analysis, infected patients appear to remain in hospital for a further 17 days. The difference in the prolongation of stay between matched and unmatched groups indicates the importance of matching as an essential model for such studies. In cases where matching cannot be performed, the median can be a good alternative measure to the arithmetic mean.
Some polymorphisms on HLA molecules are shared by different HLA types, which allows us to group HLA molecules into 'families' or groups based on the shared epitope. These cross-reactive epitope groups (CREGs) can be used as a basis for matching donors to recipients for renal transplantation. The current allocation system uses HLA-B,DR mismatching for assigning HLA points. Graft survival using newer immunosuppressive drugs still shows a significant improvement in graft survival for 0-mismatched donors (3-year survival approximately 90%) and a significantly worse graft survival for 5 and 6 HLA-mismatched donors (3-year graft survival approximately 75%). However, the difference in graft survival between 1-, 2-, 3- and 4-mismatched donors are nor significantly different from each other (80-85% survival at 3 year). This has led to a reassessment of the UNOS allocation system and the need to re-evaluate the role of HLA in graft survival, minority allocation, and HLA sensitization. One of the problems with the current algorithm is that very few recipients are actually getting well-matched kidneys (approximately 3% get 1 mismatch and 10% get 2 mismatch). Transplant centres using the UNOS CREG variance (10 points awarded for 0 CREG, 0 DR mismatches) were able to find matches at a sixfold higher rate over 0 BDR mismatches. The size of the list affects the likelihood of finding a good match and the CREG variance was more successful in larger transplant programs. The effect of HLA on equity in renal allocation is also being addressed. There is some concern that HLA points may be at least partially responsible for the decreased transplant rate in African Americans. The 1999 UNOS data showed that 46.9% of the list were Caucasian, while 55.2% of the transplants were in Caucasian recipients. Conversely, African Americans made up 35.8% of the list and only 27% of the transplants went to African Americans. Since most of the donors were Caucasian (75.9% vs. 11.2%), it has been speculated that the Black population may be disadvantaged because they have less chance of getting HLA points. The impact of HLA on transplant rate is still being disputed and may not be a major factor since so few recipients actually benefit from the points given for BDR mismatches. However, CREG matching has the advantage of equalizing the HLA effect since rare HLA antigens are grouped with common HLA antigens sharing the same public epitopes. Another advantage for CREG matching is the protection from sensitization to HLA. The effect of HLA matching on sensitization is increased with each HLA match. Black recipients are more likely to be sensitized than Caucasians with the same level of mismatch. Also, once sensitized, Black recipients are less likely to get transplanted than Caucasians because of greater difficulty in finding a well-matched donor. Of patients transplanted with 0 CREG-mismatched donors, 82% remained unsensitized to Class I, compared with less than 60% in recipients who received greater than 2 BDR mismatches. The use of CREG matching in renal allocation offers better matching to a larger group of recipients and significantly reduces sensitization to HLA.
Since September 20, 1999, our organ procurement organization (OPO) serving an ethnically diverse local distribution area has allocated kidneys using a cross-reactive group (CREG)-based variance. This variance awards 7 points for 0-CREG,0-DR mismatches and 6 points for 0-A,B mismatches in addition to points given for waiting time (3) and panel-reactive antibodies (PRA) > or = 80% (3). Previously, we have shown that awarding points for 0-CREG,0-DR mismatches in kidney allocation improves the access to HLA-matched transplants for racial groups, especially for the black race. In this study, we evaluated if there are outcome benefits as well. One- and 3-year uncensored graft survival data and analyses for the influence of HLA mismatching on graft outcome in black and nonblack recipients were provided by Scientific Registry of Transplant Recipients (SRTR). Overall, 1-year graft survival was 87.4% and not significantly different for blacks (86.1%, n = 467) vs nonblacks (88.8%, n = 730); 3-year graft survival was 74.6% and significantly lower P = .0001 for blacks (68.5%, n = 480) vs nonblacks (78.4%, n = 765). No significant advantage was observed for either the black or nonblack recipients in any of the HLA-mismatched categories, including the 0-CREG,0-DR mismatch group. An HLA matching effect also was not seen when data were stratified for patients nonsensitized (PRA < or = 10%) and sensitized (PRA > 10%) at the time of transplantation, except for the improved graft survival in sensitized nonblack recipients of 0- A,B,DR-mismatched grafts. Of the patients who lost their grafts and returned to the waiting list for retransplantation, the 0-A,B,DR mismatched were the least sensitized group (6%, n = 16), and there was a trend for less sensitization in the 0-CREG,0-DR-mismatched group (33%, n = 9), compared to those with other HLA mismatches (68%, n = 137). Thus, based on 1-year and 3-year follow-up data, there are no apparent graft outcome benefits for either CREG matching or conventional HLA matching in our service area, except for sensitized nonblack recipients receiving 0-A,B,DR-mismatched grafts. Such benefits may become more apparent with longer follow-up.