National Incidence Studies of Missing, Abducted, Runaway and Thrownaway Children (NISMART), [United States], 2011

Household Survey Addresses were obtained from the United States Postal Service (USPS) through the Delivery Sequence File (DSF) which lists all addresses that receive mail deliveries. Prior to sampling the address frame was sorted and a sample of 130,000 addresses from all 50 states and the District of Columbia was selected with equal probabilities. The address sample was fielded in five cohorts. The first four cohorts used small subsamples, totaling 15,000 addresses, to pretest different versions of the mailed screener, reminders, and invitations to improve response rates; the last cohort comprised the remaining 115,000 addresses and received the final version of these materials. Upon receiving completed screener questionnaires, eligible households were sent invitations to complete an online survey. Invited parents/caretakers who did not complete the online survey were interviewers called respondents to complete a computer-assisted telephone interview (CATI). Youth surveys for NISMART-3 were created and administered, similar to NISMART-2, but not used in analysis due to low case yield. Law Enforcement Survey The LES obtained a sample of stereotypical kidnapping cases through a survey of all law enforcement agencies (n=4,644) located in a nationally representative sample of 433 counties. Law enforcement agencies were located in the sampled counties using the 2011 National Directory of Law Enforcement Administers (www.safetysource.com), which provided a database listing all of the municipal and county law enforcement agencies and state criminal investigation agencies in the United States by address, county and other details. Agencies in the sample were sent a mail survey that asked whether the agency investigated any stereotypical kidnappings in their jurisdiction between October 1, 2010 and September 30, 2011. When agencies reported such investigations, telephone interviews were conducted with investigating officers to obtain details of the episodes.

家庭调查地址通过美国邮政署（United States Postal Service, USPS）的投递序列文件（Delivery Sequence File, DSF）获取，该文件收录所有接收邮件投递的地址。抽样前先对地址框架进行排序，随后从全美50个州及哥伦比亚特区中以等概率抽取130000个地址作为样本。
该地址样本分为5个组群开展实地调研：前4个组群采用总计15000个地址的小子样本，对邮寄式筛选问卷、提醒函及邀请函的不同版本进行预测试，以提升回复率；最后1个组群包含剩余的115000个地址，使用上述材料的最终版本。
待回收合格的筛选问卷后，向符合条件的家庭发送参与在线调查的邀请。对于未完成在线调查的受邀家长/照料者，调查员将通过电话开展计算机辅助电话访谈（Computer-Assisted Telephone Interview, CATI）。
NISMART-3的青少年问卷仿照NISMART-2的形式编制并实施，但因有效样本量过低未纳入分析。
执法机构调查（Law Enforcement Survey, LES）通过对覆盖全国代表性433个县的所有执法机构（共4644家）开展调查，获取典型绑架案件样本。本次抽样县内的执法机构名录通过2011年《全国执法机构名录》（2011 National Directory of Law Enforcement Administers，www.safetysource.com）获取，该名录提供了收录全美所有市级、县级执法机构及州级刑事调查机构的数据库，包含地址、所属县等详细信息。向抽样执法机构邮寄调查问卷，询问其在2010年10月1日至2011年9月30日期间，是否在管辖范围内调查过典型绑架案件。若机构报告存在此类调查，则对负责该案的办案人员开展电话访谈，以获取案件细节。