A Cross-Sectional Survey
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Open Access Research BMJ Open: first published as 10.1136/bmjopen-2014-005397 on 11 July 2014. Downloaded from Should both iodised and non-iodised salt be made available in Chinese cities? A cross-sectional survey JYu,1 P Liu,2 Y Liu,2 S J Liu,2 DJSun3 To cite: Yu J, Liu P, Liu Y, ABSTRACT et al Strengths and limitations of this study . Should both iodised Objective: To contribute evidence relevant to the and non-iodised salt be made policy of supplying iodised salt (IS), non-iodised salt ▪ ’ available in Chinese cities? A The article initially describes the residents pre- (NIS) or both in Chinese cities. cross-sectional survey. BMJ ferences on salt type (iodised (IS) or non-iodised Open 2014;4:e005397. Design: Subnational telephone interview survey. salt (NIS)) and their awareness of iodine defi- doi:10.1136/bmjopen-2014- Setting: China. ciency disorders and its prevention measures. 005397 Participants: Totally, 24 557 telephone numbers were ▪ The telephone interview method is biased dialled and 4833 citizens accepted the telephone towards those residents with a fixed-line tele- ▸ Prepublication history for interview. The telephone numbers were randomly phone. The pencil-and-paper interview method, this paper is available online. selected by random digit dialling and a Mitofsky- rather than computer-aided telephone interviews, To view these files please Waksberg two-stage sampling method in 17 capital was used. visit the journal online cities and 6 coastal cities from 17 iodine deficiency ▪ Options for explaining the IS/NIS choice should (http://dx.doi.org/10.1136/ disorder (IDD)-eliminated provinces (municipalities). have been more detailed. bmjopen-2014-005397). Results: The 4833 citizens finished the telephone interview. Among them, 3738 (77.3%) citizens chose elevated health awareness of the Chinese IS, 481 (10%) citizens chose NIS, and the others population, have started a debate about the chose both IS and NIS. The citizens’ awareness rates YJ and LP contributed ability of the population to make informed equally. of IDD and IDD preventive measures were 68.7% and 62.5%, respectively. choices to use iodised salt (IS) or non- Received 4 April 2014 iodised salt(NIS). As we know, some devel- Conclusions: It is not a suitable time to supply IS http://bmjopen.bmj.com/ Revised 18 June 2014 and NIS simultaneously in the developed cities of oped European countries, such as Belgium, Accepted 23 June 2014 China, but a pilot project may be conducted in the Finland, France, Germany, Greece, Ireland, cities where IDD has been sustainably eliminated, there Italy and the Netherlands, supply IS and NIS is strong awareness of IDD and the population can simultaneously in the market.5 Residents of make informed decisions regarding IS. IDD health thesecountriescanpurchaseISorNISvolun- education should be further strengthened, especially tarily. In developed cities in provinces that have regarding the potential for IQ damage. demonstrated the sustainable elimination of IDD, is it the right time to supply IS and NIS on September 24, 2021 by guest. Protected copyright. simultaneously? If so, can these populations remain free of IDD? Finally, is there a proper INTRODUCTION method to demarcate cities to which IS and Approximately 20% of the total global popula- NIS is supplied simultaneously or to which only tion resides in China, which has one of the IS is supplied? To answer these questions, the most severe iodine deficiency epidemics, in subjective preference of the residents about part due to the external environment. Iodine choosing IS or NIS and the relevant influen- deficiency disorders (IDD) were once wide- cing factors should be examined. spread and caused great damages. Universal Door-to-door interviewing is usually used salt iodization (USI) has been adopted for to conduct such investigations. Considering IDD prevention and control and has proven to the associated time and money expenditures, be an effective measure since 1994. By 2000, a cross-sectional telephone interview is a feas- 17 provinces (municipalities) in China ible alternative and is a widespread method achieved the goal of eliminating IDD and have that was adopted earlier and used by differ- For numbered affiliations see 6 end of article. sustained this outcome for 10 years based on ent countries all over the world. Successful the WHO criteria for IDD elimination.1 cases of the use of cross-sectional telephone Correspondence to However, an excess of iodine has been dis- interviewing in China include Knowledge- 2–4 Dr Sun Dianjun; covered, and new issues, including the Attitude-Practice (KAP) surveys on influenza, – [email protected] increasing rate of thyroid disease and the smoking and pollinosis.7 10 Yu J, et al. BMJ Open 2014;4:e005397. doi:10.1136/bmjopen-2014-005397 1 Open Access BMJ Open: first published as 10.1136/bmjopen-2014-005397 on 11 July 2014. Downloaded from The application of cross-sectional telephone interview- Thus, the calculated sample size was 170 responses per ing is based on educational and economic levels, in add- city; therefore, 200 responses per city were considered ition to the telephone popularisation rate. In China, by adequate: the end of 2009, the national average Urban Per Capita m2 Â p À p Disposable Income was 17 175 RMBY, and some devel- ¼ a (1 ) ð Þ oped cities (municipalities) in the IDD-eliminated pro- n d 1 vinces were most at or beyond the national average (table 1).11 Additionally, the national fixed line penetra- π δ tion had increased to 314 million people (23.5 tele- where is the positive rate and is the allowable error. phones/100 persons) and 212 million people in the cities (34.1 telephones/100 persons). These facts made telephone interview a representative and feasible way to Telephone number acquisition research the residents’ KAP towards IDD. If the fixed telephone of the neighbourhood offices in As far as we know, there were no such records about the selected district was seven-digit or eight-digit the residents’ subjective preferences between IS and numbers, the first three or four digits were deemed to be NIS, and no research on the residents’ awareness of IDD the direction code. The last four digits were obtained by in developed cities (municipalities) has been conducted the Random function (=Rand ()×10 000) in Microsoft in recent years. Hence, the National Centre for Office Excel. If the function produced randomised Endemic Disease Control (CEDC) launched this project numbers less than four digits, and ‘0’ was supplemented in April 2010, with the aim of obtaining data on the in front of the generated numbers. The number of tele- above aspects to decide whether supplying IS and NIS phone numbers created randomly should be at least five simultaneously is feasible in developed cities in times the effective sample size, that is, at least 1000 tele- IDD-eliminated provinces. The methods and results may phone numbers should be created per city. provide evidence or references for similar regions in the world. Quality control The research was approved by the review board of the Harbin Medical University. Participant consent was METHODS acquired when they answered the telephone. The survey City sites to be investigated programme and survey result database were designed The 17 capital cities of the 17 provinces (3 municipal- and delivered to the project cities by the national CEDC. ities, 6 coastal provinces and 8 inland provinces) that The survey programme was improved based on a pilot http://bmjopen.bmj.com/ had achieved the goal of IDD elimination in 2000 were survey, and the questionnaire had clear questions that selected (table 1). One coastal city was also selected in prompted simple answers and avoided providing hints to each of the above coastal provinces. A total of 23 cities the residents. Sensitive questions, such as age, were were included in the study. designed as “Which age group do you belong to? <20, 20–30, 30–40…”. Target population In the programme, the investigation was carried out in Citizens who had fixed telephones in the 23 selected a unified manner, including the order and pattern of cities. the questions, the dialling time (18 :30–21:00), and on September 24, 2021 by guest. Protected copyright. instructions for making notes of the answers and filling The main contents of the questionnaire the database. ▸ If IS and NIS are supplied simultaneously, which will To avoid investigation and report biases and to you choose? And why? improve the research participants’ cooperation, the ▸ Have you heard of IDD? If so, what are the effects? interviewers were trained on their attitude, mood and How is IDD prevented? countermeasures in case of emergency by the project ▸ Can you tell us your occupation and age group? provinces themselves according to the rules of the survey programme. For example, some related questions put Sampling method and sampling size forward by residents could be answered only after the Random digit dialling and the Mitofsky-Waksberg two- interview was finished to avoid bias. stage sampling method were used in this study.12 In each To guarantee the reliability of the research informa- city, only the main urban zones were investigated, and tion, a return visit was conducted after a project city fin- two districts were selected randomly from each main ished the telephone interviews. The quality control urban zone. At least 200 effective samples were sampled officer of the provincial Centre for Disease Control in each city included in the survey. The sample quota (CDC) or CEDC visited the citizens who had accepted was divided evenly between each district. The sample the interview. At least 10% of the respondents were ran- size was calculated according to formula 1; the positive domly sampled to complete the return visit question- response rate (π) was approximately 70% according to naire.