Mexican National Survey on Organized Violence
Methodological Note

Author: Carlos López, Project Manager
Translation: Esther Schlosser

February, 2014

1. SAMPLE SELECTION AND FIELDWORK OF GENERAL POPULATION SURVEY

1.1 General description

A national survey was carried out based on a probabilistic representative sample that allows to generation of estimations applicable to the behaviour of the totality of the population of interest. In this context, the population of interest or universe was composed of Mexican citizens of age 18 and above who reside within the national territory at the time of the survey.

In accordance with the study’s purpose, the sample size was designed to be sufficient for a stratified analysis. The criteria used for the stratification was the level of homicidal violence. The data were based on annual homicide rates per 100 thousand inhabitants at the municipal level (average rates for three years from 2009 to 2011). We took the homicide data from the National System of Health Information (sinais) at the Secretary of Health (www.sinais.salud.gob.mx). The municipal population data come from the INEGI Population and Household Census of 2000 and 2010 (www.inegi.org.mx). The table above presents the distribution of municipalities and inhabitants along the five strata of homicidal violence.

Strata
	Homicide rate intervals
(Ø 2009–2011)	Level of
violence	#
Municipalities	#
Population	% 
Municipalities	% 
Population	
1	6	Very low	1002	23,152,185	40.8	20.6	
2	More than 6 to 10	Low	351	22,494,352	14.3	20.0	
3	More than 10 to 15	Medium	302	26,648,330	12.3	23.7	
4	More than 15 to 30	High	402	21,842,359	16.4	19.4	
5	More than 30	Very high	399	18,199,312	16.2	16.2	

1.2. Sampling method

The design of the sample used the electoral sections of the Electoral Federal Institute (IFE) as sampling frame.

The sample had multiple stages, the electoral sections were the Primary Sampling Units (UPM). As the first stage of selection, the UPMs were arranged by size (by the amount of registered voters in each section) in every one of the five strata of violence to later generate a simple randomly placed starting seed for the first UPM conglomerate.
After the starting seed selection from the first UPM conglomerate, a systematic criterion was applied to each of the next UPM conglomerates; this process was repeated until we had achieved the totality of starting points, necessary to complete the required sample inside each stratum. Inside every selected UPM, the same number of interviews were applied, 10 interviews, in the case of this study. During the second sampling stage, at least 2 blocks from each UPM (electoral section) were randomly selected, these blocks were the Secondary Sampling Units (USM). In each USM a variable amounts of interviews, yet never more than five, were held according to its conditions of geography and urban distribution.

Following a simple random method, the USMs were selected, based on the maps of electoral sections generated by IFE and INEGI. The third sampling stage was the selection of households, which were the Third Sampling Units (UTM). Each of the UTMs was selected following a systematic method by block front according to the home density of each USM.

In every UTM only one person was interviewed. The person had to be over 18 years of age, a resident of the chosen address and hence of that household. The selection of this person, which was the last stage of the sampling process, was random with a final quota adjustment, serving as parameters the population distribution by sex and age from the 2010 Census.

According to the research requirements, the size of the national sample of 2,400 cases has an approximate margin of error of +/- 2.0%; the margin of error within each stratum was of +/- 4.5%. The table below presents the sample distribution by strata: 

Stratum	Sample Size	Margin of error	
Very low violence	480	+/-4.5	
Low violence	480	+/-4.5	
Medium violence	480	+/-4.5	
High violence	480	+/-4.5	
Very high violence	480	+/-4.5	
National Total	2400	+/-2.0	

People from 5903 homes had to be contacted to complete the 2400 cases, which implies a 59% rate of non-responses. It is important to mention that the refusal rate was higher in urban areas and in those areas where people had higher insecurity perceptions.

1.3 Fieldwork

The interviews were held from October, 26th to November, 30th 2013. All of them were applied as personal interviews in the selected homes by the sampling process. Only one interview to a adult member of the household was considered. 68 pollsters, 10 supervisors, 18 capturers, 2 analysts and 1 project director participated in the implementation of the interviews. 

On October, 23rd, in Mexico City, a training session with coordinators, supervisors and the local pollster team was held. Between October 24th and ,31st additional training sessions were held in the regional headquarters of the local teams: Culiacán, Guadalajara, Irapuato, Monterrey, Mérida, Querétaro, Tijuana and Veracruz.

The interviews had an average duration of 35 minutes. The attitude of participants was, in general, friendly and participatory. It was very helpful to mention that the sponsors were academic institutions; it facilitated the communication and lowered the distrust. The people interviewed found the topics of the interview interesting, some interviewees added data about personal histories and/or of their communities related to criminal violence.

Regarding the problems the teams faced in the field, we would like to emphasize the substitution of communities in starting points 139 and 140 in Michoacán (both are urban electoral sections in the municipality of Morelia) where the pollsters were robbed and assaulted by people who said to be “in control” of the area, and their work material was taken from them. These points were replaced by the adjacent neighborhood, with similar social and demographic features, where the work could be done. Point 13 in Campeche (rural area, locality La Libertad from the municipality Escárcega) was replaced due to lack of access, because the road to the sampling area was closed; it was replaced by the last locality (San Juan) to which there was access through that road. Another incident, which did not imply the need of a substituting a starting point, happened in Torreón, where the pollster was robbed by armed persons. This happened on the public transportation on the way to the working area (starting point 17, urban electoral section, Los Ángeles neighborhood). Luckily, no mayor incidents were reported from our fieldwork team.

1.4 Data processing

Data processing was carried from December 2nd to December 9th 2013. All data were captured with the CSPRO software. A “double capture” was implemented in order to have additional quality control of the data. Over all, the percentage of capturing errors was very low, equivalent to 0.09%. The few mistakes detected were corrected in their totality. The table below presents the totality of errors from the sample, separated and detailed by binder (capturer):

Capturer	Number of cases	Number of corrections	Number of captured data	% of errors	Average number of capturing errors per interview (1698 data per interview)	
binder 1	60	118	101880	0.116	2.0	
binder 2	80	115	135840	0.085	1.4	
binder 3	50	95	84900	0.112	1.9	
binder 4	50	94	84900	0.111	1.9	
binder 5	40	89	67920	0.131	2.2	
binder 6	80	130	135840	0.096	1.6	
binder 8	60	107	101880	0.105	1.8	
binder 9	30	83	50940	0.163	2.8	
binder16	660	918	1120680	0.082	1.4	
binder 10	80	136	135840	0.100	1.7	
binder 11	30	60	50940	0.118	2.0	
binder 12	40	83	67920	0.122	2.1	
binder 13	110	184	186780	0.099	1.7	
binder 14	110	188	186780	0.101	1.7	
binder 15	500	895	849000	0.105	1.8	
binder 17	360	576	611280	0.094	1.6	
binder 18	60	125	101880	0.123	2.1	
Total	2400	3996	4,075,200	0.098	1.7	

2.  SAMPLE SELECTION AND FIELDWORK OF ELITE SURVEY

2.1 General description
To add to the results of the general population, a shortened and adapted version of the questionnaire was applied to a limited sample of leaders from different sectors of Mexico’s public life. 

The category of Mexican elite members includes people with managerial positions or influence who directly participate in decision making processes within their professional sector or field of activity. 

2.2. Sampling method

The study contemplates the classification of leaders from the following six key groups:

1.	Government: high and mid-range public officials from Secretaries of State of the federal government, state governments (including governors and cabinets) and of the parastate sector and decentralized agencies; 
2.	Politicians: legislators and party leaders at the federal and state levels;
3.	Entrepreneurs: entrepreneur and managers from medium and large sized enterprises in Mexico;
4.	Media: executives and journalists from print and electronic media, national as well as local (newspapers, magazines, news agencies, radio and television stations);
5.	Academics: members of the National System of Researchers (SNI) and/or professors from the mayor public and private universities; all fields of knowledge are included;
6.	Civil society: high-level representatives of religious groups, labor unions, business organisations, professional associations, and non-governmental organizations (NGOs). 

The study contemplated the application of at least 100 interviews for each sector, to get a final sample of 600 valid interviews. The selection was made through a random draw in each sector, using leader directories elaborated by Data OPM. The final size of the sample consists of 629 cases. 

2.3 Fieldwork
The interviews were applied via telephone from the central offices of Data OPM by a professional and trained team with experience in this kind of elite interviews. A signed letter by the authorities of CIDE was sent to each potential participant within the sample, in which they were invited to participate in the study by answering the telephone survey, whose purpose was explained in this letter. The interviews were held from November, 4th 2013 to February, 6th 2014. 22 pollsters, 2 supervisors, 11 capturers, 1 analyst, and 1 project manager participated in the realization of the interviews. To complete the 629 cases, a total of 18, 225 invitations were sent out.

2.4 Data processing
Data processing was carried out from December, 9th 2013 to February, 10th 2014. The data were captured with the CSPRO program. A “double capture” was implemented in order to have additional quality control of the data. Over all, the percentage of capturing errors was very low, equivalent to 0.21%. The few mistakes detected were corrected in their totality. The table below presents the totality of errors from the sample, separated and detailed by binder (capturer):

Capturer	Number of cases	Corrected data	Number of captured data	% of errors	Error average by captured interview (1698 data per interview)	
binder 1	133	551	223307	0.247	4.1	
binder 2	122	283	204838	0.138	2.3	
binder 3	113	260	189727	0.137	2.3	
binder 4	56	189	94024	0.201	3.4	
binder 5	13	70	21827	0.321	5.4	
binder 6	13	68	21827	0.312	5.2	
binder 8	48	178	80592	0.221	3.7	
binder 9	22	162	36938	0.439	7.4	
binder16	34	87	57086	0.152	2.6	
binder 10	40	99	67160	0.147	2.5	
binder 11	34	36	57086	0.063	1.1	
Total	322	1178	540638	0.216	3.7	

IMPORTANT NOTICE:

It would be appreciated that once used the appropriate citation information is made, so send requested full document reference, article, book, and/or investigation report made by it, as well as mentioning the(s) database(s) BIIACS data that was (were) used.

To facilitate sending appointments to BIIACS is necessary to provide the information in the form below http://www.biiacs.cide.edu/node/add/citation