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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.

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Introduction: Ruminant responses are one of the most important cognitive feature in people with depression and cause disruption of thinking, problem solving and social relationships. The aim of this study was to compare the effectiveness of "Solution-Focused Brief Therapy" and "Compassion-Focused Therapy" on ruminant responses of couples with depression. 
Methods: The method of the present study was quasi-experimental with a pretest-posttest design with a control group. The statistical included all couples with depression who referred to the Mehregan Javan Comprehensive Health Center of Mashhad, Saadabad ward in 2019, the number of which was 150 couples. According to the inclusion criteria, 45 couples were selected as the sample. The sampling method was targeted and convenience. After selecting the available sample populations by simple random sampling method, the sample individuals were selected. The samples included the first intervention group "Solution-Focused Brief Therapy" (15 couples), the second intervention group "Compassion-Focused Therapy" (15 couples) and control group (15 couples). Data collection instruments included a demographic questionnaire, the "Ruminative Responses Scale". Content validity was measured by qualitative method, face validity and reliability by internal consistency method by calculating Cronbach's alpha coefficient. For the first intervention group 6 sessions, each session was held between 1.30 to 2 hours and for the second intervention group 8 sessions 1.30 to 2 hours. Data were analyzed in SPSS. 24. 
Results: The results showed that "Solution-Focused Brief Therapy" reduced the expression of thoughts (P<0.001, F=91.51), thinking (P<0.001, F= 62.70), depression (P<0.001, F=104.19) and ruminant responses (P=0.001, P=0.001) have a significant effect on post-test and follow-up. In addition, the findings showed that "Compassion-Focused Therapy" reduced the expression of thoughts (P<0.001, F=22.21), thinking (P<0.001, F=50.39), Depression (P<0.001, F=93.93) and ruminant responses (P<0.001, F= 54.51) have a significant effect on post-test and follow-up. The results of post hoc test comparing the two groups showed that in the post-test phase, there was a significant difference between the two groups in reducing the variable in the thought of immersion (P>0.003). Also, there is no significant difference between the two treatment groups in reducing the score of thought expression variables, depression and rumination responses in the post-test and follow-up stages. 
Conclusions: "Short-Term Solution-Oriented Therapy" and "Compassion-Focused Therapy" are effective in expressing thoughts, thinking and depression, as well as the overall score of the ruminant responses of couples with depression. It is recommended that the above treatment methods be used to reduce or eliminate the ruminant responses of couples with depression.