Iranian Journal of

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Background & Objectives: This investigation was prompted by the growing importance of nested case-control studies and the increasing frequency with which they are done in epidemiologic research. After a brief explanation of nested case-control studies, we evaluate the trends in research methodology over the last decade, especially with regard to cohort, case-control, and nested case-control designs.
Methods: Data for this study were extracted from the PubMed database, using these keywords: Nested Case-Control, Risk-Set Sampling and Density Sampling. The search was confined to the 10-year period from 1996 to the end of 2005. As for other methodologies, we used keywords Cohort and Case-Control for a search over the same time period. The search itself was performed on April 25, 2006.
Results: We found 2011 articles reporting nested case-control studies. There were 95 such articles in 1996 the number had increased to 289 in 2005. Case-control and cohort designs accounted for 68456 and 60479 articles, respectively. The number of case-control articles rose from 4378 in 1996 to 10270 in 2005, while that of cohort articles increased from 2981 to 9771 over the same period.
Conclusions: The number of cohort and nested case-control articles followed similar upward trends over the last decade and their rate of increase was greater than that of simple case-control articles.

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Background and Objectives: Children immunization program is one of the most successful and most cost-effective public health interventions and medical programs. The study was designed and conducted in order to assess the vaccination coverage in areas covered by Tehran University of Medical Sciences (TUMS).

Methods: This study was a cross-sectional study of children aged 24 months to 6 years living in urban areas and high-risk and marginal areas covered by TUMS. Six hundred and thirty children were sampled in 90 clusters in urban areas and cluster sampling as probability proportional to size sampling was performed in high risk areas and a sample size of 768 children was determined. The questionnaires were completed by interview.

Results: In high risk 750 children (97.7%, 95% CI: 96.32-98.60%) and 616 children (97.8%, 95% CI: 96.3-98.78%) in urban areas had complete immunization histories. Furthermore, 98.4% of the Iranian children and 95.0% of foreign children (P=0.019) in marginal areas and 98.1% of the Iranian children and 92.1% of the foreign children (P=0.046) in urban areas had complete immunization histories.Ignorance of immunization program (%50) was addressed as the main reason for incomplete immunization.

Conclusion: Universal mass vaccination coverage of the children and equal coverage in marginal and urban areas indicated the success of the authorities in the implementation of this program. Organizing training courses for mothers on the immunization program, providing the required facilities and services, monitoring and supervision of vaccination and also considering the immunization status of foreign children seem to be essential in maintaining and improving the existing status.