Sampling

Sampling Procedure

The sample for the Iraq Multiple Indicator Cluster Survey was designed to provide estimates on a large number of indicators on the situation of children and women at the national level; for areas of residence of Iraq represented by rural and urban (metropolitan and other urban) areas; for the18 governorates of Iraq; and also for metropolitan, other urban, and rural areas for each governorate. Thus, in total, the sample consists of 56 different sampling domains, that includes 3 sampling domains in each of the 17 governorates outside the capital city Baghdad (namely, a metropolitan area domain representing the governorate city centre, an other urban area domain representing the urban area outside the governorate city centre, and a rural area domain) and 5 sampling domains in Baghdad (namely, 3 metropolitan areas representing Sadir City, Resafa side, and Kurkh side, an other urban area sampling domain representing the urban area outside the three Baghdad governorate city centres, and a sampling domain comprising the rural area of Baghdad). 

The sample was selected in two stages. Within each of the 56 sampling domains, 54 PSUs were selected with linear systematic probability proportional to size (PPS). 

\After mapping and listing of households were carried out within the selected PSU or segment of the PSU, linear systematic samples of six households were drawn. Cluster sizes of 6 households were selected to accommodate the current security conditions in the country to allow the surveys team to complete a full cluster in a minimal time. The total sample size for the survey is 18144 households. The sample is not self-weighting. For reporting national level results, sample weights are used.


The sampling procedures are more fully described in the sampling appendix of the final report and can also be found in the list of technical documents within this archive. 

(Extracted from the final report: Central Organisation for Statistics & Information Technology and Kurdistan Statistics Office. 2007. Iraq Multiple Indicator Cluster Survey 2006, Final Report. Iraq.)

Deviation from Sample Design

No major deviations from the original sample design were made.  One cluster of the 3024 clusters selected was not completed all othe clusters were accessed.

Response Rates

Of the 18144 households selected for the sample, 18123 were found to be occupied. Of these, 17873 were successfully interviewed for a household response rate of 98.6 percent. In the interviewed households, 27564 women (age 15-49 years) were identified. Of these, 27186 were successfully interviewed, yielding a response rate of 98.6 percent. In addition, 16570 children under age five were listed in the household questionnaire. Of these, questionnaires were completed for 16469 which correspond to a response rate of 99.4 percent. Overall response rates of 97.3 and 98.0 are calculated for the women's and under-5's interviews respectively.

Weighting

The Iraq Multiple Indicator Cluster Survey sample is not self-weighted. Essentially, by allocating equal numbers of households to each of the sampling domains, different sampling fractions were used in each sampling domain since the size of the sampling domains varied. For this reason, sample weights were calculated and these were used in the subsequent analyses of the survey data.
The major component of the weight is the reciprocal of the sampling fraction employed in selecting the number of sample households in that particular sampling domain:
Wh = 1 / fh
The term fh, the sampling fraction at the h-th stratum, is the product of probabilities of selection at every stage in each sampling domain:
fh = P1h * P2h * P3h
where Pih is the probability of selection of the sampling unit in the i-th stage for the h-th sampling domain.

Since the estimated numbers of households per enumeration area prior to the first stage selection (selection of primary sampling units) and the updated number of households per enumeration area were different, individual sampling fractions for households in each enumeration area (cluster) were calculated.  The sampling fractions for households in each enumeration area (cluster) therefore included the probability of selection of the enumeration area in that particular sampling domain and the probability of selection of a household in the sample enumeration area (cluster). 
A second component which has to be taken into account in the calculation of sample weights is the level of non-response for the household and individual interviews. The adjustment for household non-response is equal to the inverse value of:
RR = Number of interviewed households / Number of occupied households listed
After the completion of fieldwork, response rates were calculated for each sampling domain. These were used to adjust the sample weights calculated for each cluster. 
Similarly, the adjustment for non-response at the individual level (women and under-5 children) is equal to the inverse value of:
RR = Completed women's (or under-5's) questionnaires / Eligible women (or under-5s)
Numbers of eligible women and under-5 children were obtained from the household listing in the Household Questionnaire in households where interviews were completed.
The unadjusted weights for the households were calculated by multiplying the above factors for each enumeration area. These weights were then standardized (or normalized), one purpose of which is to make the sum of the interviewed sample units equal the total sample size at the national level. Normalization is performed by multiplying the aforementioned unadjusted weights by the ratio of the number of completed households to the total unadjusted weighted number of households. A similar standardization procedure was followed in obtaining standardized weights for the women's and under-5's questionnaires. Adjusted (normalized) weights varied between 0.110 and 3.721 in the 56 sampling domains.
Sample weights (Table SD.4) were appended to all data sets and analyses were performed by weighting each household, woman or under-5 with these sample weights. 

(Extracted from the final report Appendix A: Central Organisation for Statistics & Information Technology and Kurdistan Statistics Office. 2007. Iraq Multiple Indicator Cluster Survey 2006, Final Report. Iraq.)
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