Power calculation for cohort studies with improved estimation of expected numbers of deaths

Summary This paper focuses on improving the accuracy of sample size calculations for cohort studies by careful calculation of the expected number of deaths in the population, taking into account either prior information or realistic assumptions about variables which may affect the mortality or incidence. Sometimes small changes in the assumptions can dramatically alter the expected numbers and may necessitate modifications in the design of the study. Possible modification include extension of the follow-up time, and recognition that the real strength of the study may lie in the potential for pooling several similar studies. The problem will be discussed with reference to two examples of occupational cohort studies where differing prior information was available.

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Zusammenfassung Diese Arbeit beschäftigt sich mit der Genauigkeit der Berechnung des Stichprobenumfangs in Kohortenstudien, wenn detaillierte Berechnungen für die erwartete Zahl der Verstorbenen berücksichtigt werden. Dies kann entweder durch die Ausnutzung vorhandener Informationen oder durch realistische Annahmen über die Faktoren, die Mortalität oder Inzidenz beeinflussen, geschehen. Schon kleine Unterschiede in diesen Annahmen kann die erwartete Zahl der Verstorbenen erheblich verändern und es notwendig machen, das Design einer Studie zu verändern. Solche Modifikationen bestehen z.B. in der Verlängerung der Follow-up Zeit der Studie oder in der Einsicht, dass es nötig ist, Daten aus mehreren Studien zusammenzufassen. Die Probleme werden anhand von zwei Beispielen aus dem Bereich der Berufsepidemiologie diskutiert.

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Résumé Cet article concerne la précision des estimations de taille d'échantillons pour les études de cohortes. Le calcul précis du nombre de décès attendus dans la population prend en compte les variables susceptibles d'affecter la mortalité ou l'incidence, provenant soit d'une connaissance préalable, soit d'hypothèses réalistes. De modestes changements d'hypothèses peuvent parfois altérer de façon substantielle les nombres attendus et nécessiter des modifications dans le protocole de l'étude. Parmi les modifications possibles, il faut citer la prolongation du temps de suivi de l'étude ainsi que le constat que la valeur réelle de l'étude pourrait reposer sur la possibilité de mise en commun de plusieurs études similaires. Le problème est discuté à l'aide de deux exemples d'études de cohortes professionnelles pour lesquelles différentes informations préalables sont disponibles.

     

A comparison of tympanic thermometer readings to pulmonary artery catheter core temperature recordings

The purpose of this study was to determine the accuracy of FirstTemp (Intelligent Medical Systems, Carlsbad, CA) tympanic thermometer readings compared with core body temperatures obtained via pulmonary artery catheter (PAC). Five measurements were obtained on 19 cardiovascular surgery patients. Tympanic thermometer measurements tended to be higher than PAC measurements. However, most of the differences were not clinically significant. Differences found between right and left ear measurements were most likely due to poor measurement technique. When the correct technique is used, nurses can be confident that tympanic temperature readings are clinically accurate.     

Symptomatic treatment in the fragile X-associated tremor/ataxia syndrome.

There is no established treatment for the neurological features of the recently discovered fragile X-associated tremor/ataxia syndrome (FXTAS). Fifty-six patients with FXTAS completed a questionnaire to determine whether any medications had been effective for neurological symptoms. Of 11 subjects with definite FXTAS, 8 (70%) were on medications for their neurological symptoms, whereas most subjects with possible or probable FXTAS, 31 (70%) of 45 subjects, were not on medications. Although no therapy was uniformly effective for intention tremor, ataxia, Parkinsonism, memory loss, or anxiety, some subjects with intention tremor or Parkinsonism reported improvement with medications frequently used in other movement disorders. Overall, all 22 subjects on medications reported improvement in one or more symptoms. Lack of insight, recall bias, and cognitive impairment may have resulted in an underestimation of the beneficial effect of medical therapy. This study suggests that patients with FXTAS can derive improvement from medication treatment for some of their symptoms.     

Plasticity of human motion processing mechanisms following surgery for infantile esotropia

Monocular oscillatory-motion visual evoked potentials (VEPs) were measured in prospective and retrospective groups of infantile esotropia patients who had been aligned surgically at different ages. A nasalward-temporal response bias that is present prior to surgery was reduced below pre-surgery levels in the prospective group. Patients in the retrospective group who had been aligned before 2 yr of age showed lower levels of response asymmetry than those who were aligned after age 2. The data imply that binocular motion processing mechanisms in infantile esotropia patients are capable of some degree of recovery, and that this plasticity is restricted to a critical period of visual development.     

Cyclooxygenase-2 expression in the endometrium and its relationship to bleeding in users of continuous oral contraceptives.

OBJECTIVE: The objective of the present study was to investigate whether or not the presence of irregular bleeding during use of oral contraceptives (OC) is associated with increased cyclooxygenase-2 (COX-2) expression. PATIENTS AND METHODS: An observational study was carried out in 26 patients who were using gestodene 75 microg/ethinylestradiol 30 microg prior to endometrial resection. The patients were divided into two groups: those with amenorrhea (n = 14) and those who had irregular bleeding (n = 12). The resected endometrium was immunostained for COX-2, Bcl-2 and Ki-67 expression. Routine pathology was carried out using standard hematoxylin-eosin staining. RESULTS: Irregular bleeding during OC use was associated with strong COX-2 expression in both glandular and superficial epithelium. There were also more patients in this group with irregular endometrial maturation and higher Ki-67 values. Bcl-2 expression, on the other hand, was not affected by the presence of uterine bleeding. CONCLUSION: The presence of irregular bleeding during OC use is associated with strong COX-2 expression in the endometrium, thereby suggesting a pivotal role of prostaglandins in this process.     

Multicolored Asian lady beetle hypersensitivity: a case series and allergist survey.

BACKGROUND: Multicolored Asian lady beetles (Harmonia axyridis) have been used as a biological control agent against crop-destroying aphids in the United States. Outside their natural habitat, H. axyridis seeks refuge in homes during fall and winter, leading to patient complaints and symptoms of rhinitis, wheezing, and urticaria on exposure to the beetles. OBJECTIVE: To gain a better understanding of the character and spectrum of allergic disease provoked by exposure to home-infesting lady beetles. METHODS: Eight patients with allergic symptoms suspected of being caused by H. axyridis and consistent with an IgE-mediated process were identified and interviewed. A whole-body extract from H. axyridis was prepared. Western blots using the patients' serum identified specific IgE antibodies in the extract. Through a novel technique, immunohistochemical analysis using beetle sections overlayed with patient serum was performed. A random survey of allergists from across the United States was also performed to evaluate experience with cases of lady beetle allergy. RESULTS: Western blots revealed IgE binding to 5 proteins with molecular weights of approximately 8.6, 21, 28, 31, and 75 kDa. Specific IgE bound to proteins localized in the beetle's mouth and leg areas. The allergist survey revealed positive responses in North Central, Mid-Atlantic and New England states. CONCLUSION: In 8 patients with allergic symptoms on exposure to high levels of lady beetles, specific IgE bound to proteins from H. axyridis. There was also an increased frequency of suspected cases of lady beetle allergy in endemic areas.     

Papilledema in obstructive hydrocephalus caused by giant cell astrocytoma of tuberous sclerosis.

A 5-year-old girl with progressive hemiparesis and headache was found by brain imaging to have a large tumor centered at the foramen of Monro, blocking cerebrospinal outflow and producing massive lateral ventriculomegaly. Total excision of the mass led to a pathologic diagnosis of giant cell astrocytoma. Dermatologic abnormalities had been detected shortly after birth but were unexplained. Abdominal imaging disclosed renal cysts, and ophthalmologic examination disclosed papilledema and retinal plaques. On this basis, a diagnosis of tuberous sclerosis (TS) was finally made. Two months after surgery, papilledema had resolved, and visual function appeared to be normal. Although the patient apparently escaped visual loss, other reports affirm that giant cell astrocytoma, a common tumor in TS, may go undetected for long enough to produce irreversible optic neuropathy from chronic papilledema. Because patients with TS may not report visual loss, they should undergo periodic ophthalmologic screening.     

Dentoskeletal treatment changes in Class II subdivision malocclusions in submentovertex and posteroanterior radiographs.

The objective of this study was to evaluate the dentoskeletal changes consequent to orthodontic treatment in subjects with Class II subdivision malocclusions, treated with asymmetric extractions, compared with a normal-occlusion control group. The sample consisted of 3 groups, with 30 subjects in each: normal-occlusion subjects (group 1), untreated Class II subdivision subjects (group 2), and Class II subdivision patients treated with asymmetric extractions (group 3). All subjects had a full complement of permanent teeth at the beginning of treatment. The average ages of the subjects were 22.42, 15.76, and 18.57 years, respectively, in groups 1, 2, and 3. Measurements of relative differences in the spatial position of dental and skeletal bilateral landmarks were obtained from the submentovertex and posteroanterior cephalometric (PA) radiographs. The t test for independent samples was used to compare group 1 with groups 2 and 3 at different times. Results from the submentovertex radiograph showed that asymmetric extractions in Class II subdivision malocclusions will maintain the differences in the anteroposterior positions of right and left, maxillary and mandibular first molars, as would be expected with the treatment protocols used. There were no significant skeletal changes that could be attributed to the treatment approaches investigated or transverse collateral effects with the asymmetric mechanics used. It was also demonstrated that treatment of Class II subdivision malocclusions with asymmetric extractions produced corrections of maxillary and mandibular dental midline deviations with the midsagittal plane, without canting the occlusal plane or any other investigated horizontal plane, as seen in the PA radiograph. Treatment of Class II subdivision malocclusions with asymmetric extractions constitutes a beneficial approach to this problem.     

Cyclooxygenase 2 expression in serous tumors of the ovary.

This study was designed to investigate the expression of cyclooxygenase (COX)-2 in ovarian serous tumors (benign, borderline tumors, and carcinomas) and primary peritoneal serous carcinomas. Cases diagnosed between 1995 and 2001 were reviewed; 47 benign tumors, 6 borderline tumors, and 39 carcinomas were examined, as well as 12 normal ovaries that served as controls. Blocks were stained with anti COX-2 polyclonal antibody and staining was graded qualitatively. The staining intensity was assessed as weak (score of 1), moderate (score of 2), or strong (score of 3). Normal ovarian and tubal epithelium, inclusion cysts, benign serous tumors, and borderline tumors had a uniform score 3 staining pattern. Serous ovarian carcinomas had variable staining scores, tending to correlate with the level of tumor differentiation. Well-differentiated carcinomas had more intense COX-2 staining than poorly differentiated carcinomas, which had only weak COX-2 staining. The degree of COX-2 staining was not significantly related to overall survival. In conclusion, COX-2 expression is present in serous tumors, including benign tumors, borderline tumors, and carcinomas. Similar to the findings in other neoplasms, COX-2 expression is strongest in well-differentiated tumors and is much less evident in those that are poorly differentiated. The clinical utility of these findings is related to the potential role of nonsteroidal anti-inflammatory drugs, which are COX-2 inhibitors, in treating and/or preventing some forms of ovarian carcinoma.