Journal of School of Public Health and

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Background and Aim: Case-Control studies provide evidence in the area of health. Validity and accuracy of such studies depend to a large extent on the similarity (similar distributions) of the case and control groups according to confounding variables. Matching is a method for controlling or eliminating the effects of important confounders. Matching using propensity score has recently been introduced to control the effect of confounders, especially when there are many of them in a study.

Materials and Methods: Matching according to propensity score was used in a genetic association study-a case-control study involving 300 subjects-to assess the effect of candidate genes on Alzheimer's disease in the Iranian population. Propensity score was calculated using STATA.8 software age, sex, education level, job and genetic background were included in the model to calculate the score.

Results: A total of 385 blood samples were taken from the participants. We managed to extract DNA in 155 of the 173 case subjects and in 161 of the 212 control subjects. The model for propensity score was statistically significant. Of the total of 316 DNA samples, 302 were matched based on their calculated propensity scores, while the individual matching method could only deliver 28 pairs.

Conclusion: The propensity-score matching method results in selection of a larger number of pairs, as compared with the conventional individual matching method. We propose to use this method, which also ensures a similar distribution of confounders between the case and control groups, particularly when there are limitations in the number of subjects available for matching.

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Background and Aim: Application of modern technologies and changes in industries and work practices, particularly in assembly lines, have resulted in increased work-related musculoskeletal disorders (MSDs). This has led to reduced occupational competence in both industrialized and developed countries. This study was conducted to determine the prevalence of MSDs in the upper limbs, postural loading on the upper limbs (using the LUBA technoque), and ergonomic risk factors among assembly workers of an Iranian Telecommunications Manufacturing Company (ITMC) in Shiraz, Iran.

Materials and Methods: In this cross-sectional survey data were collected, using the Nordic Musculoskeletal Disorders Questionnaire (NMQ) and LUBA Checklist, on 193 randomly selected registered assembly workers from 8 units of the assembly line of ITMC, Shiraz, Iran. The statistical tests used were as follws: 1.The qui-square test, to determine factors causing MSDs 2. One-way analysis of variance and Kruskal-Wallis to determine postural loading index 3. Logistic multiple regression analysis, to determine risk factors.

Results: Lower-back symptoms were found to be the most prevalent problem (67.9%.) among the workers. The findings also showed that the upper limb disorders were significantly associated with age, sex, job, daily working time, work evironment conditions, and twisting (P<0.01). Based on LUBA, a large majority of the workers (89.64%) had experienced high postural loading (PLI = 5). In addition, significant associations were found between postural loading and symptoms of upper limbs and units of work (P <0.05).

Conclusion: Based on these findings, MSDs are prevelent among Telecommunication Manufacturing Company in Shiraz, Iran. The most important factors likely to cause MSDs are postural loading on the limbs and unfavourable working conditions. Interventional programs aimig at preventing musculoskeletal problems among assembly line workers should focus on reducing postural loading.