GLOBAL TOBACCO SURVEILLANCE SYSTEM Global Youth Tobacco Survey Training Workshop Introduction to the GYTS Sample Design & Weights

Outline  Overview of GYTS survey design & sample selection – Target population – Design specifications & sample selection  Sampling design development – Sampling parameters worksheet – School enrollment list  Use of PC Sample software  Sample weighting procedure – Based on GYTS sample design and weights manual No change in original GYTS sample design and selection

Cycle of Statistical Activity in GYTS Surveys Population: (Which rates to be estimated; and for whom) Sample Design: (Probability sampling; to meet country’s information needs) Selected Sample: (Collect data from survey respondents) Analysis Findings: (Produce design-based estimates of rates)

Cycle of Statistical Activity in GYTS Surveys Population: (Which rates to be estimated; and for whom) Sample Design: (Probability sampling; to meet country’s information needs) Selected Sample: (Collect data from survey respondents) Analysis Findings: (Produce design-based estimates of rates)

GYTS Target Population  School-based survey of students aged 13–15 years – By sampling grade range that includes this age group – Typically possible grade range 8-10  Nationally representative – National scope is the standard – To enhance consistency of findings among GYTS countries by making the scope of findings the same – Geographic scope may be limited to subareas of the country (e.g., certain regions, proximity to the capital city) & require clear justification  Includes students in public and private schools – Especially important if private/public school tobacco use differs substantially – Inclusion of private schools depends on the availability of lists of these schools – Require a clear justification if private schools are excluded

Sample Sizes and Expected Precision  GYTS surveys are designed to produce nationally representative estimates, by gender, with a minimum student sample size of 1,500 from a minimum of 20 schools – A student sample size of at least 1,500 is recommended for each domain (e.g., region/province or school type) when estimates are to be reported for these domains by gender – Larger the sample sizes in terms of schools and students, higher the precision of estimates with lower margin of error  GYTS sample design should adjust for potential nonresponse and ineligibility at each stage – School participation rate – 80% – Student attendance rate – 80%

Cycle of Statistical Activity in GYTS Surveys Population: (Which rates to be estimated; and for whom) Sample Design: (Probability sampling; to meet country’s information needs) Selected Sample: (Collect data from survey respondents) Analysis Findings: (Produce design-based estimates of rates)

GYTS Sample Design Specifications  Sampling is school based – Linkage to the target population via the schools attended by members of the target populations  Two stage sample design 1.Schools selected proportional to enrollment size  Largest schools “self-representing” (i.e., selection probability = 1)  Stratification implicit from PPS systematic selection  Explicit stratification as needed (e.g., by region, urban/rural, etc.)  Schools with fewer than 40 students may be excluded 2.Classrooms chosen randomly within selected schools  All age-eligible students in selected classes eligible to participate

Sample Design Development  Sampling parameters worksheet – Implementing agency & contact – Scope of the survey – Type of schools – Type of sampling – Grades included & sample size – Grade & school level associated with age group years – Requirements of sample selection – Small school preference – GYTS coordination with other survey – Materials needed – Expected date for receiving school enrollments & fieldwork period – Any other specifications

Sample Design Development  School enrollment list – School ID – School identification address – Province/state – Region – Type of school (private/public) – Grades taught – Level of school (e.g., primary, secondary or high) – Enrollments by grade and sex – Total school enrollments in eligible grades – Any other specifications

Sample Selection Using PC Sample  School selection using PC Sample software – Within- school selection worksheets  Selection of schools using probability proportional to school enrollment size – School ID uniquely identify a school from the list – Uses PPS systematic sampling – Measure of size is the number of eligible students in each school – Certainty (self-representing) schools based on sampling interval – Re-compute the sampling interval for selection of the remaining schools  Selection Classes and Students – Produces school-level forms and class-level forms for selection of classes – Generate sequence of systematic random numbers for class selection within each selected school  All the students in the class completes the survey

Input files for PC Sample School Enrollment List

Output files from PC Sample School Selection List

Output files from PC Sample School Level Sample Information Form

Class Selections Using School Level Sample Information Form

Output files from PC Sample Class Level Sample Information Form

GYTS Sample Weighting Process  Sample weights – Base weight from student selection probability – Nonresponse adjustment (at school, class & student levels) – Calibrate the sample to the demographics of the target population of students (by grade and sex)  Weighted sample used to produce analysis findings – Estimates of tobacco use prevalence & key tobacco control indicators – Computing 95% CI’s using complex sample design features – Stratification and PSU will be identified for variance estimation based on certainty and non-certainty schools in the sample

Sample design development: RC, MoH/MoE, and technical experts Send sample parameters worksheet & school enrollment list templates to IA [RC] Selection of schools & send school and class- level sample information forms to IA [RC] Following instruction on school and class- level sample information forms for implementation Send completed school and class-level sample information forms for weighting and data analysis WHO/CDC work with IA [RC] to review and finalize sample design Sample Design Development Process Process is confidential & at any stage the sample design, in part or full, should not be disclosed or without the prior approval/permission from the IA [RC] & CDC

Agenda for Sampling Breakout Session Finalize sample design development & process  Review and finalize sampling parameters worksheet – Scope, target population & key reporting sub-groups – Assess potential for coordinating GYTS with another survey  Review school enrollment list

GLOBAL TOBACCO SURVEILLANCE SYSTEM Global Youth Tobacco Survey Training Workshop Introduction to the GYTS Sample Design & Weights