Evidence-based medicine (EBM) stresses the examination of evidence from clinical research and describes it as a shift in medical paradigms, in contrast to intuition, unsystematic clinical experience, and pathophysiologic rationale. While the importance of randomized trials has been created by the concept of the hierarchy of evidence in guiding therapy, much of the medical research is observational. There is competition, contrast, and a feeling of inferiority and uselessness for observational studies, created by a lack of understanding of medical research. However, observational studies and randomized clinical trials (RCTs) can be viewed as the steps of observation and experimentation that form the basis of the scientific methodology. Further, rational healthcare practices require knowledge about the etiology and pathogenesis, diagnosis, prognosis, and treatment of disorders. The reporting of observational research is often not detailed and clear enough with insufficient quality and poor reporting, which hampers the assessment of strengths and weaknesses of the study and the generalizability of the mixed results. Thus, design, implementation, and reporting of observational studies is crucial. The biased interpretation of results from observational studies, either in favor of or opposed to a treatment, and lack of proper understanding of observational studies, leads to a poor appraisal of the quality. Similar to the Consolidated Standards of Reporting Trials (CONSORT) statement for the reporting of randomized trials, the Strengthening of the Reporting of Observational Studies in Epidemiology (STROBE) statement was developed with recommendations to improve the quality of reporting observational studies. The STROBE statement consists of a checklist of 22 items, which relate to the title, abstract, introduction, methods, results, and discussion sections of articles. Multiple types of observational studies are conducted; however, 3 types have been highlighted in the STROBE document and also in the present review, which include cohort studies, case-controlled studies, and cross-sectional studies. This comprehensive review provides an introduction and rationale, types, design, and reporting of observational studies; outcomes assessment and data presentation and analysis; statistical analysis, results, and a discussion of observational studies. Key words: Observational studies, cohort studies, case control studies, cross-sectional studies, allocation bias, sample size, Strengthening of the Reporting of Observational Studies in Epidemiology (STROBE)

Ninety-three standing anteroposterior (AP) pelvis roentgenograms in 87 patients were measured for a total of 186 normal hips in children aged 1-17 years. For each hip, the physeal angle relative to the floor, the physeal angle relative to the pelvis, the cartilage thickness perpendicular to the floor, and the cartilage thickness perpendicular to the physis were measured and recorded. The physeal angle varied from ages 1-7 years, stabilizing at age 8 at a mean of 23 degrees . Physeal angle is best measured relative to the floor because pelvic obliquity introduces significant variability to the measurements. Cartilage thickness ("joint space") declined after age 7 years, with measurements in three statistically distinct groups. There was a statistically significant difference between cartilage-thickness measurements of boys versus girls, with girls showing a slightly smaller cartilage thickness than boys. Cartilage thickness measured perpendicular to the floor was not statistically significantly different from that measured perpendicular to the physis. We describe and recommend standard measurement techniques for physeal angle and cartilage thickness. These established normal values may be helpful in the diagnosis and evaluation of coxa vara and chondrolysis, and in identifying the head at risk for slipped capital femoral epiphysis or Legg-Calvé-Perthes disease.

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DNA replication in dividing eukaryotic cells imposes a requirement for the faithful recreation on the newly synthesized chromatids of the nucleoprotein architecture of parent chromosomes. Practically nothing is known about the structure of postreplicative immature chromatin (a very short-lived entity of <30 min.). We report here the unexpected discovery that during DNA amplification of locus II/9A in salivary gland polytene chromosomes of the fungus fly Sciara coprophila, DNA replication fork passage is uncoupled from postreplicative chromatin assembly; this enables visualization and analysis of chromatin fibers disassembled by DNA replication. We used electron microscopy to visualize a wealth of low nucleosome density immature chromatin fibers in preparations of Sciara chromatin from amplification-stage tissue. Remarkably, as gauged by high sensitivity to micrococcal nuclease and an unusually short length of DNA associated with each histone octamer, we found that locus II/9A which undergoes amplification and is replicated once every 4-6 hrs. (but not the bulk genome or a replicatively quiescent DNA stretch) was maintained in such an ummature fiber for ca. 24 hrs. Following amplification, locus II/9A assumed conventional chromatin organization, indicating that the epigenetic mark targeting nascent DNA to the chromatin assembly machinery is stable for several hours. We propose that this very unusual prolonged maintenance of a segment of the genome in immature chromatin facilitates access by the basal transcriptional machinery to the amplified DNA, and thus is an evolutionary adaptation to the demand for high transcription from genes that reside in the amplified loci.

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