Purpose: Hidden caries is a term used to describe occlusal dentine caries that is missed on a visual examination, but can be detected by bitewing radiographs. The aim of this study is the review of new studies about this lesion and presentation the ways for diagnosis, prevention and treatmen of this lesion.Review of Literature: Investigations believe that the etiology of this lesion is the morphology of occlusal fissures and also topical fluoride use. Diagnosis of hidden caries is difficult and need to use the diagnostic tools such as bitewing radiographs. Investigators have shown the prevalence of hidden caries is between 1.4% to 15% of occlusal surfaces of permanent molars that have diagnosed as sound teeth. Prevention of this lesion is taken by fissure sealing soon after eruption and treatment is taken by amalgam or composite restoration. It is suggested to investigate about the prevalence of hidden caries in our country.

Sampling hidden populations is challenging due to the lack of convenience statistical frames. Since most populations exposed to special diseases are hidden and hard to reach, sampling methods that produce representative and efficient samples from the populations have become a study subject for researches all over the world. Because of the unknown probability of selecting samples in conventional sampling methods and also invalidity of generalizing the results of non-probability sampling methods to the statistical population, the necessity of introducing probability chain-referral sampling methods, such as the respondent driven sampling method becomes imperative. In this article, besides introducing the respondent driven sampling method, some of the advantages of this method as relative decrease of the bias of estimates, declining the non-response rate by paying incentives and allocating weights proportional to reciprocal of the social network size of respondents to produce unbiased estimates are described. Moreover, some disadvantages of this method such as lack of producing differential samples by selecting similar seeds, lack of reaching more efficient method than snowball sampling by implementing this method improperly and lack of achieving to equilibrium by existing weak social networks among members of interested population are stated. Another aim of this article is to compare sampling methods of hidden population with the respondent driven sampling method which are the results of implementing this method in different surveys and existing simulations.

Introduction: Around two decades ago, the Respondent Driven Sampling (RDS) method was introduced to sample hidden populations especially those exposed to high risk diseases. This study is aimed to determine factors affecting the design of sampling method for hidden populations exposed to high risk diseases.Methods: In this review article, in addition to introducing the RDS method, 11 surveys that employed this method to study hidden populations are reviewed. Consequently, the key points that should be considered in designing this method including formative assessment and seeds selection are studied.Results: Results indicated that if the main purpose of a formative assessment and seeds selection does not achieve the hidden population parameter estimates will differ actual values and the survey would counter some biases. Uncertainty of recruiter’s degree, not-forming long recruitment chains, and slowly recruiting of recruiters could be the most important of these biases.Conclusions: Without paying attention to the influential considerations in designing RDS method, this method in sampling hidden populations will not be applicable. It is recommended that researchers in order to guarantee the successful penetrating to the target hidden population, consider the key influential points RDS method in advance.

In this paper, the epidemiological researches on addiction and drug use in Iran were reviewed from the methodological perspective. Specifically, the methods of estimating the number of drug users were evaluated and criticized. Bias is an important problem in these researches, specially selection and measurement bias. These types of bias mostly provide an underestimation.

Background: A detailed study of hidden and hard to reach populations in order to identify their characteristics is essential because they endanger the health of the society by their dangerous behaviors. However, sampling in these populations through conventional sampling methods is impossible due to reasons such as being hidden and lacking a precise frame.Methods: In this article, applicable concepts and key points in the implementation of respondent driven sampling were defined by focusing on designs that aimed to study dangerous and hidden behaviors such as dangerous sexual behavior, injecting drug abuse, and HIV infection.Findings: The merits of the respondent driven sampling are the production of unbiased and effective estimations of necessary parameters in populations at risk of rare and hidden diseases in comparison to other chain referral and conventional sampling methods, and the innovations of this sampling method during its implementation.Conclusion: The application of the respondent driven sampling method in order to achieve unbiased and precise estimates of the prevalence rate of rare and hidden diseases is recommended in health programs of the society.

To investigate the effect of vermicompost, N fertilizer and their integration on growth, biological and essential yields oil and its components in two populations (Varamin and Isfahan), an experiment was conducted in a randomized complete block design with three replications in the field of Isfahan Medicinal Plants Research Center in 2016. Fertilizer treatments including 100% urea, vermicompost 33.3 and urea 66.6%, vermicompost 66.6 and urea 33.3%, 100% vermicompost and control treatment (without fertilizer) as the first factor and Varamin and Isfahan populations as the second factor were selected. The results showed that the interaction effects of nitrogen fertilizer and populations on all studied traits were significant. In both populations, nitrogen fertilizer improved height, biological and essential oil yields, content of essential oil compounds (d-Carvone and its yield, α-phellandrene and linalool; except p-Cymene and Limonene in Isfahan population). Since in medicinal plants, the quantity (biological yield) and quality (essential oil and d-Carvone; the most important ingredient and the highest amount of essential oil in this experiment), 66.6% vermicompost + 33.3% urea in Varamin population, was the best treatment in the experiment. In addition an in the direction of human health and sustainable agriculture, it is possible to reduce 33% of chemical fertilizers application and pollution; however, in terms of other essential oil contents (α-phellandrene, Linalool and p-Cymene), 100% vermicompost fertilizer treatment was superior in Isfahan population.