Author’s response to reviews Title: Status of dental caries and associated factors in Tibetan adults: findings from the fourth China National Oral Health Survey Authors:

1. L 12, please replace "correlates" to "associated factors". A: The "correlates" had been replaced by "associated factors". Line 6 in Page 3. 2. L. 15 the authors mention: "A multistage stratified random cluster-sampling method was used to enroll participants from three groups (35-44, 55-64, and 65-74 years old) recommended by the World Health Organization." Please remove the affirmation "WHO information", as age 55-64 is not within the recommended ages for surveys. A: Thank you very much for your careful review on our manuscript. We have corrected this error. Line 11 and line 12 in Page 3. 3. Please replace the "+-" to "SD (standard deviation)" throughout the manuscript. A: the "+-" throughout the manuscript had been removed. And in abstract section the revised version was as follows: The mean DMFT (SD) was 7.62(4.84), 12.46(8.16), and 21.38(8.93). 4. Please add the number of individuals evaluated in this study (results). A: Number of individuals evaluated in this study has been added in the participant section of abstract. Line 19 to line 21 in Page 3. 5. The conclusion is not supported by your results (please see my comment on the 'discussion'). A: Thank you for your comment. We revised the conclusion as: The status of dental caries in the adults in Tibet is severe and the treatment rate is very low. The study suggests a correlation between crown caries and the variables age, level of education and frequency of tooth brushing; correlation between root caries and residence, income level, frequency of tooth brushing and exposed root surfaces. These findings could be as reference to develop community based interventions to reduce the prevalence of caries in Tibet. 6. Please remove the keyword "risk", as this causal relationship has not been evaluated in the present study. One suggestion is to insert the descriptor "observational study". A: We have removed "risk" and inserted "observational study" as the key word. Introduction: 1. In the first paragraph, the authors describe the global burden of dental caries and oral diseases around the world. I suggest including more recent revisions. A: Thank you for the recommended journals. These two latest systematic reviews clearly analyzed the burden of oral disease especially caries are very heavy. We have added these two journals as he reference of our study. 2. Some passages and paragraphs in the introduction lack references. Please check. A: Two references (Aacute EDB, N-Aguilar, Malvitz DM, Lockwood SA, Rozier RG, Tomar SL. Oral health surveillance: past, present, and future challenges. J PUBLIC HEALTH DENT. 2003(No.3):141-9. Lu HX, Tao DY, Lo ECM, Li R, Wang X, Tai BJ, et al. The 4th National Oral Health Survey in the Mainland of China: Background and Methodology. The Chinese journal of dental research : the official journal of the Scientific Section of the Chinese Stomatological Association (CSA). 2018 2018-01-01;21(3):161.) have been added in the introduction. These two references described the effect of national and regional oral health surveys on assess oral health and needs, explore disparities between regions, and plan intervention programs and policies at national and local levels. 3. I suggest the insertion of the conceptual hypothesis, as it guides the investigation itself. A: Thank you for your suggestion. We consider that this was the first national oral health survey in Tibet and decided that only describe the primary objectives. 4. I suggest following the "STROBE guidelines" to report the study. A: Thank you for your suggestion. We have referred to "Strengthening the Reporting of Observational Studies in Epidemiology (STROBE): explanation and elaboration".[J]. Annals of internal medicine,2007:W163~W194. The manuscript has been revised. Methods: 1. I suggest a greater contextualization of the region in which the sample was obtained. Provide more details such as the number of inhabitants, as well as the number of individuals in the assessed age groups. A: More detailed about Tibet has been described in paragraph 2 of the section ‘Study design and sample selection’. And number of each assessed age group was provided in sample selection. 2. This manuscript used data from a countrywide survey (fourth National Oral Health Survey of China). However, information about the sample size calculation for the outcome of this study is vague and confusing: what were the parameters considered for sample calculation? What was the minimum sample size to satisfy such requirements? According to what the authors describe, the required sample is much larger (4,320) than the one included in the study (n = 476). A: Thanks for your kindly inquiry. Our study used the data from a countrywide survey (fourth National Oral Health Survey of China). The fourth National Oral Health Survey of China was aiming to determine the prevalence and risk factors of common oral diseases such as dental caries and periodontitis. According to previous study in Tibet, the prevalence of dental caries was greater than 95% among people over 44 years old[1]. The prevalence of dental caries was not the primary research variable in our study. Our study was aimed to determine the DMFT values in different age groups (35-44, 55-64 and 65-74) and different areas (Urban and Rural). Besides, the associated factor analysis was based on the DMFT values. So the sample size was estimated according to the DMFT and DF-root values as the cross-sectional study. The NCSS PASS 11 was use to calculated the sample size. A minimum sample size of 64 in each group should produce a two-sided 95% confidence interval with the precision that is equal to 2.5 when the estimated standard deviation is 10.0(from the third National Epidemiological Survey of Oral Health)[2]. According to our sampling results in Table 1, the minimum sample size was 66, which satisfied the minimum sample size requirements. 3. What does RMB mean? Please explain the acronym and compare the value with dollars. A: RMB means Ren Min Bi, the legal tender of the People's Republic of China. ¥ 1 is approximately US$0.14. 4. It is necessary to explain how the covariables were collected, categorized and further used in the statistical analysis. Please provide references for the adopted categories (for example the knowledge and attitude of oral health). A: The categories of covariables were explained in section of ‘Questionnaire survey’, and we added references about the adopted categories. Thanks for your suggestions. 5. The authors write "characteristics of the baseline." For me, this term refers to the idea of more points in time. Please remove the term baseline throughout the manuscript. A: we have removed the term baseline throughout the manuscript. 6. L. 58 "Since all baseline characteristics were coded as categorical variables, we first used Chisquare test to identify potential factors correlated with higher odds of crown and root caries. The variables with significant P value (P<0.05) was then selected and included in binary logistic regression model to examine their independent associations with crown and root caries." Why? Based on what variables with p <0.05 in the Chi-square test are included in the Logistic Regression? I suggest reviewing this issue. In addition, the logistic regression model has been adjusted? A: Thanks for your suggestion. We had redone the univariate and multiple logistic regression analysis for all the potential factors for the high DMFT and DF-root value (>75th percentile DMFT value as cut-off and DF-root≥1). When we performed the multiple logistic regression, the model was adjusted for sex, age and residence. The results were listed in the new table 3 and table 4. 7. I suggest performing unadjusted and adjusted regression. In addition, check if logistic regression is the best option (read about Poisson Regression). Ref: Barros, A. J., & Hirakata, V. N. (2003). Alternatives for logistic regression in cross-sectional studies: an empirical comparison of models that directly estimate the prevalence ratio. BMC medical research methodology, 3(1), 21; A: Thanks for your kindly suggestions. Both of the unadjusted and adjusted regression had been done in this revised manuscript. In addition, considering that this was a multi-stage complex sampling, the multiple logistic regression was applied for the adjusted regression with the Survey logistic procedure of SAS 9.4 (SAS Institute, Cary, NC). The multilevel structure of the sample: individual (level 1) nested into the community/cluster (level 2) were considered as the strata variables in the logistic regression model. 8. In the statistical analysis, the authors used a logistic regression model to assess the predictors of the outcomes. However, sampling was carried out by clusters (districts or communities, for example). Statistical analyses should consider the multilevel structure of the sample: individual (level 1) nested into the community/cluster (level 2). Multilevel models provide the estimation of contextual effects of neighborhood-level variables by accounting for spatial clustering of individuals within areas [Snijders; Boske, 2003]. In this sense, the occurrence of caries can be influenced by the environment where they live. The analysis should be remade considering this factor.  Snijders, T. A. B., & r, R. J. (2003). Multilevel analysis: An introduction to basic and advanced multilevel modeling. London: Sage. A: Thanks a lot for your thoughtful suggestions. Considering this was a multistage stratified random sampling technique, the multilevel structure of the sample: individual (level 1) nested into the community/cluster (level 2) should be evaluated in the logistic regression. We had redone the logistic regression. The multiple logistic regression was applied for the adjusted regression with the Survey logistic procedure of SAS 9.4 (SAS Institute, Cary, NC). The areas and the communities were considered as the strata variables, that should eliminated the influe