Box-Behnken design: an alternative for the optimization of analytical methods.

The present paper describes fundamentals, advantages and limitations of the Box-Behnken design (BBD) for the optimization of analytical methods. It establishes also a comparison between this design and composite central, three-level full factorial and Doehlert designs. A detailed study on factors and responses involved during the optimization of analytical systems is also presented. Functions developed for calculation of multiple responses are discussed, including the desirability function, which was proposed by Derringer and Suich in 1980. Concept and evaluation of robustness of analytical methods are also discussed. Finally, descriptions of applications of this technique for optimization of analytical methods are presented.

[Prevalence of thyroid nodules in 40 years-old or old women]. / Prevalência de nódulos de tireóide detectados por ecografia em mulheres após os 40 anos.

OBJECTIVES: Thyroid nodules constitute a very common clinical problem and the differential diagnosis includes thyroid cancer. As thyroid cancer is rare, it is important to know the prevalence of thyroid nodules in cohorts strongly predisposed to this problem to be able to measure its impact on the health care system, and to devise appropriate diagnostic strategies. The aim of this study was to determine the prevalence of thyroid nodules in women 40 year-old or older by echography. METHODS: Between August 1996 and December 1997, 207 women, 40 year-old or older, were consecutively evaluated by thyroid echography in the Radiology Division of the Hospital de Clínicas de Porto Alegre. Patients who came to the Division to be submitted to thyroid echography were excluded. The mean age of patients studied was 54.7 years (median: 53, range: 40-86 years). One hundred and twenty three patients (54.9%) had a normal thyroid and eighty-two had an abnormal gland (39.6%). Thyroid nodules were detected in seventy-three women (35.3%) and these were larger than 1 cm in 35 women (16.9%). Women without thyroid nodules were younger (53.1 +/-10.7 years) than women with thyroid nodules (58.2 +/-10.6 years) p=0.001; and the prevalence of any thyroid nodule (p=0.001) or nodules larger than 1 cm (p=0.007) increased with age. CONCLUSIONS: Thyroid nodules are very common in women 40 year-old or older, their prevalence increases with age in this cohort and these nodules are potentially palpable (larger than one cm) in one of six women in this age group It is important to have these data in mind when ordering thyroid echographic studies in women 40 year-old or older.