1.Describe the primary sampling units (PSU) and secondary sampling units (SSU) used in country C and in Kinshasa province in the study by Burnett et al.

 2.The Kinshasa province survey described in Burnett et al. had 3 sampling stages, what was the third sampling stage (hint: look under “Survey Objectives and Sample Size”?)

​As this study consists of two sample sizes thus, the third sampling stage needed to include both the study groups of age 6-11 months old infants and 12-23 months children. With secondary Stage Unit as 15 neighborhoods selected by systematic probability proportional to estimated size methods, the third sampling stage was inclusion of 180 HH per clusters with approach of every fourth house for the 6–11-monthold survey. However, in HHs with >1 child aged 12–23 months; one of the children was randomly selected.

3. Based on the definitions of probability sampling and sampling frame found in the 2015 Vaccination Coverage Survey Reference Manual (section 3.6, section 6.2 and annex A),​ what do you think of the sampling frames used in country C vs. the sampling frame used in the survey described by Burnett et al.? Describe potential limitations of the frames used and how they may relate to sampling bias

• Sampling frame for country C

In each stage of sampling, sampling frame has been selected through the facilitation of MoH, from National Statistics Office with inclusion of inclusion of the clusters from urban, semi-urban, and rural areas in the sample, the sampling frame will be stratified by urban, semi-urban, and rural areas.

1st stage sampling: The list of Enumeration areas with their number of households will be used as a sampling frame for the EPI survey to select the primary sampling units or clusters.

2nd stage sampling: The list of households in the selected clusters or EAs will be used as a sampling frame to randomly select the required 22 households from each cluster using systematic random sampling methodology.

• Potential limitations and relation to sampling bias

As this study targets two different study population, mothers of children 0-11 months of age and of age and the EPI coverage survey cover children aged 24-35 months, the sampling has focused mainly on EPI coverage survey on children aged 24-35 months. Biasness regarding the same mother with children 24-35 and also 0-11 months has not been clearly mentioned. What is the inclusion criteria for mother of 0-11 months not clearly mentioned. In 2.3 Target population: children 12-34 months of age is mentioned while in sample design 24-35 months of age is mentioned (I am confused). Also, Potential limitation may be time factor as the study also covers HH with no eligible children and mothers. Selection of list of HH in second stage of sampling would lead to potential bias as the selection would be prepared by the fieldwork team.

• Sampling frame for survey used in Burnett et al.

List of neighborhoods with the estimated target population were provided for each of the 12 zones of interest, based on polio micro plan data compiled in 2013–2014. Also neighborhoods listed in the sampling frame had unknown boundaries, making it difficult to use neighborhoods to inform sampling of HHs.

• Potential limitations and relation to sampling bias

Possible bias because of local record-keeping practices, staff turnover, and the limitations of recall.

4.In the Kinshasa province survey described in Burnett et al., the expected sample size was not reached. The authors describe two potential factors that may have contributed to this. How could have this been prevented? What are the main consequences of not reaching the expected sample size?

The potential factors that contributed to not reaching expected sample size could have been prevented by conducting two studies with different objectives and target groups independently with separate data collectors.

Although this study could identify factors associated with vaccination status but was not able to explore methodological considerations for linked survey implementation due to the mentioned limitation of study as the expected sample size was not reached.