Survey ID Number
NGA_2021_NLPS_v01_M
Title
National Longitudinal Phone Survey 2021-2022, Phase 2
Weighting
BASELINE (ROUND 1): In order to produce national estimates from the successfully interviewed sample, weights must be applied to the information provided by sampled households. Weights for the GHS-Panel serve as the basis for the Nigeria NLPS surveys, but the weights must be adjusted to reflect the selection and interviewing process. The weights for the Nigeria NLPS were calculated in several stages.
1) Begin with the GHS-Panel full sample household weights.
2) Apply an adjustment factor for the selection into the frame (GHS-Panel households that have contact details for a household member). A ratio adjustment was applied at the Zone-level (the strata for the GHS-Panel) to preserve the sum of household weights within each Zone between the full GHS-Panel sample and the NLPS frame.
3) Apply an adjustment for selection into the NLPS sample. The adjustment is a simple expansion factor that is the inverse of the selection probability from the frame for each sampled unit.
4) Apply an adjustment factor for non-contact of sampled households. This was again performed with a ratio adjustment at the Zone-level.
5) Apply an adjustment factor for non-response of contacted households through a ratio adjustment at the Zone-level.
6) Calibrate the weights (following adjustments 2-5) according to the properties of the full weighted GHS-Panel sample. This calibration step adjusts the weights such that the estimates obtained from the final NLPS sample will match the weighted means of the full GHS-Panel sample for specified characteristics. The calibration was performed using only information obtained from the GHS-Panel interview and thus will only reflect changes in the sample composition and not changes over time. The calibration applied here aims to correct for selection bias that is introduced at any point between identification of the frame and the final successfully interviewed sample. Selection bias is of particular concern in phone surveys since some segment of the population does not have access to a phone and there are more difficult barriers to successfully reach and interview households over the phone. The calibration was applied using the ReGenesees package in R. The characteristics included in the calibration were numerous, reflecting different dimensions of household socioeconomic status that were correlated with nonresponse. Characteristics include consumption expenditure, household size sex of household head, marital status of the household head, age of the household head, education of the household head, working status of the household head, asset ownership, access to electricity, improved water source, improved sanitation facilities, access to financial services, land ownership, agricultural activities, as well as demographic breakdown according to sex and 8 age groups (0-6, 7-14, 15-24, 25-34, 35-44, 45-54, 55-64, and 65 years and older). The weights were also applied to the total number of households in the population given by the GHS-Panel weights.
7) Trim the weights. Outlier weights were trimmed at the 1st and 99th percentiles using the ReGenesees package in R which adjusts the weights to given bounds while minimizing the deviation from the estimates obtained from the calibration in step 6.
In subsequent rounds of the survey, steps 4, 5, and 6 will be applied to the final baseline weights.
The baseline (round 1) weights are located in the household-level data file (p2r1_sect_a_2_5_6_9a_12.dta) under the variable name wt_p2round1.
ROUND 2: In Round 2, several different weights are provided: one at the household-level and three at the individual-level. The household weights are the same as was provided in previous round. For the household weights, the baseline (round 1 of phase 2) weights were adjusted for noncontact and nonresponse as well as calibrated following the same procedures outlined in Round 1 (steps 4, 5 and 6). The round 2 household weights can be found in the household-level data file (p2r2_sect_a_2_2a_2b_6_12) in the variable named wt_p2round2.
Given the focus on individual migration information in round 2 and the selection steps outlined above for the sample of adult members, an additional three individual-level weights were calculated and provided in the round 2 data. The individual weights for the migration module were calculated according to:
w_ish=w_h×(n_hs/N_hs )^(-1)
Where w_ih is the sampling weight for individual i who is sex s (male or female) in household h, w_h is the final household level weight (i.e., wt_p2round2), N_hs is the total number of eligible adult household members (15 years or older) of sex s in household h and n_hs is the equivalent number of selected eligible individuals in the household. The individual weights were then calibrated to correspond to the sex and age distribution of the total adult population according to the post-harvest visit of the GHS-Panel. The age groups considered in the calibration were 15-24, 25-34, 35-44, 45-54, 55-64, and 65 years or older, all further disaggregated by sex (male/female).
The basic individual weight described above is the cross section individual weight that considers all individuals that migration information was collected on. This weight is called wt_migr_p2r2 and can be found in the individual-level data file (p2r2_sect_2_2a). However, an additional two weights are provided for the panel of individuals interviewed in the GHS-Panel wave 4 and round 2 of the NLPS Phase II (i.e., excluding individuals added in any round of the NLPS). The first weight (wt_migr_p2r2_pp_panel) contains the weight for individuals interviewed in the post-planting visit of the GHS-Panel wave 4 and the second (wt_migr_p2r2_ph_panel) contains the weight for individuals interviewed in the post-harvest visit of the GHS-Panel wave 4.