Weighting

When the data of the sample survey are expanded to the total population, each household included in the sample is given a statistical weighting which characterizes the total number of households represented by the selected household. The average value of basic weighting is 600 i.e. Each selected household is a representation of about 600 households.

The following factors are used for constructing a basic weighting:

Probability of selecting each big city, small town and village council.

Probability of selecting each constituency in big cities/small towns and the zone in village councils.

Probability of selecting each household within the constituency and the zone included in the sample.

The inverse value of the product of the three probabilities is the basic weighting of a household:

1

WB_k = -------------------- ,

p1_k * p2_k *p3_k

where

k is the number of a household.

The total of all basic weightings gives the estimate of the number of all household of the country and is constant during the whole year:

sum_(i= 1 to n ) WB_k = N ,

where

n is the size of sample;

n is the estimate of the total population.

The earlier described method of constructing a household sample did not take into account that some households will not be surveyed for one or the other reason such as impossibility to get the household at home despite numerous attempts, illness, categorical refusal to provide information or for other reasons. If the estimate comprises only the households that agreed to be surveyed, the results of the survey will be understated.

There are different methods of making adjustments for missing answers. One of them is the adjustment of basic weighting i.E. Statistical re-weighting which is based on overstating the weighting of respondents having certain characteristics which are peculiar for those who refused from participating in the survey.

Based on checking the data the variables are selected which will be then used for statistical re-weighting such as :

region.

Place of residence (big city, small town, village).

Type of accommodation (individual apartment, individual house, communal flat, part of a house, hostel).

Size of the household (single individuals and households consisting of 2, 3, 4 and more people).

ADJUSTMENT OF BASIC WEIGHTING FOR NON-RESIDENTIAL APARTMENTS - During the baseline interview there might be a situation when the selected apartment is non-residential (it can be used as a shop, office premises and etc.). As the addresses of such apartments were accounted for when forming a sample (i.E. They influenced the probability of selecting other addresses), it is needed to adjust basic weightings to eliminate distortions. To enhance the accuracy of calculations, all selected households are divided into groups depending on regional location. These groups are called weighting units. Basic weightings are thus adjusted in accordance with the formula:

sum_(j= 1 to L_k )WB_k_j + sum_(j= 1 to M_k )WB_k_j

WV_k, = --------------------------------------------------------------------------------- ,

sum_(j= 1 to M_k )WB_k_j

where

k = 1,7 is the number of the region;

WV_k_i is the weighting of the “i” household of the “k” region adjusted for non-residential apartments;

WB_k_i is the basic weighting of the “i” household of the “k” region;

L_k is the number of non-residential apartments in the “k” region;

M_k is the number of the rest of the households in the “k” region.

ADJUSTMENT FOR NON-ANSWERS DURING THE BASELINE INTERVIEW - To make an adjustment for non-answers in the baseline interview, the weighting units are formed based on the following characteristics:

the region, 7 values (the Brest region, ..., the Mogilev region); type of settlement, 3 values (big city, small town, village); type of accommodation, 2 values (individual accommodation (an individual apartment in big cities and small towns and an individual house in villages) or other type of accommodation (communal flat, part of a house, hostel); size of a household, 4 values (1 person, 2 persons, 3 persons, 4 and more persons). After the units are formed, the distribution of households is analyzed in a way that one unit should contain at least 20 households. The new weightings are then calculated based on the modified units. For the “i” household included in the “k” unit, the weighting WBL_ki adjusted for non-answers in the baseline interview can be

sum_(j= 1 to M_k )WV_kj + sum_(j= 1 to N_k )WV_kj

WBL_ki = ----------------------------------------------------------------------- * WV_ki ,

sum_(j= 1 to N_k )WV_kj

where

WV_k_i is the weighting of the “i” household included in the “k” weighting unit adjusted for non-residential apartments;

M_k is the number of non-answers per a baseline interview in the “k” unit;

N_k is the number of answers per a baseline interview in the “k” unit.

In 1996 after an adjustment for non-answers in the baseline interview the average weighting increased to 692.

ADJUSTMENTS IN QUARTERLY INTERVIEWS - The units for an adjustment for non-answers in quarterly interviews are formed based on the same characteristics which are used for the baseline interview. For the “i” household included in the “k” unit formed for the quarter, the weighting WQ_alpha_k_i adjusted for non-answers in the quarterly interview is calculated in as follows:

sum_(j= 1 to M_k )WQ_a - 1_kj + sum_(j= 1 to N_k )WQ_a - 1_kj

WQ_a_k_i = ---------------------------------------------------------------------------------------------- * WQ_a - 1_ki ,

sum_(j= 1 to N_k )WQ_a-1_kj ,

where

a= 1,2,3,4 is the number of the quarter;

WQ_a-1_k_i is the weighting adjusted for non-answers in the quarterly interview for the quarter a-1 for the “j” household included in the “k” unit formed for quarter a and WQ_0_ki ;

M_k is the number of non-answers in the quarterly interview in the “k” unit for quarter a;

N_k is the number of answers in the quarterly interview in the “k” unit for quarter a.

After the baseline interview the average weighting has slightly increased due to high percentage of answers after the first interview. The average weightings are equal to 708, 716, 723 and 726 accordingly for 4 quarters in 1995. It should be noted that the households who miss one interview are withdrawn from the survey. Thus the households who answered the questions of the last interview had also answered the questions of all previous interviews. Therefore, the weighting calculated for the last interview can be used for the households who answered the questions during the whole year. The annual report uses the data on the households who answered the questions during the whole year re-weighted by means of using the last quarter weighting.