M ETHODOLOGY , S URVEY D ESIGN AND D ATA C OLLECTION
4.3 Sampling Frame and Sample Selection Procedure
The study area (i.e. geographic boundary) of this research is restricted to Dhaka City, the capital of Bangladesh on the bank of the Buriganga River (the study area can be seen on Map 2.3 in Chapter Two). Considerable differences exist about where the boundary of Dhaka City lies. Various utility, service organizations and departments have demarcated it for their own purposes4. The demarcation of the Dhaka City Corporation (DCC) is applied mainly because BBS has adopted this demarcation for their Population Census which is used for this study’s sample frame.
3The reasons are discussed in details later in Section 4.7.3.
4 The Dhaka metropolitan area defined by the RAJUK is 1508 sq km which includes Savar, Tongi, Gazipur, Narayanganj and Keranigang. The DWASA service area is 380 sq km. The DCC area is 360 sq km. The BBS also uses the concept of statistical metropolitan area (SMA) with an area of 1530 sq km which is an agglomeration of the DCC, four other adjacent municipalities (e.g. Narayanganj, Tongi, Gazipur and Savar), several cantonments and a
Dhaka City, as defined by the DCC5, is comprised of 14 thanas6 and each thana in turn contains about 4 to 17 wards. In total, there are 90 wards as per the 1991 statistics7. Each ward is again divided into a few mohallas. Each mohalla contains one or a few streets and a varying number of households. Altogether, there are 659 mohallas and the total number of households in Dhaka City is 643,016 (BBS, 1993). A description of the target population and selected samples is provided in Table 4.2. Both population and survey data are divided into ‘Buriganga River area (BRA)’ and ‘outside Buriganga River area (OBA)’8.
In selecting a sample from this target population of the survey, the important consideration was how to identify or select the respondents among the population (i.e. from more than 643 thousand households). One of the options would have been to use the voters’ list. However, during the period of the sample frame design and survey, a new voters’ list was being prepared to be used in the October 2001 general election and it was considered as a ‘confidential document’ at that stage. Furthermore, although in many studies the voters’ list has been used as a sampling frame, it was not considered a reliable sample frame because the unit of analysis in this study is the household (the voters’ list contains only the individual adult population).
Table 4.2: Profile of population and sample at a glance
Total of DCC Selected for survey Name
of thana Ward Mohalla Household Ward Mohalla Household
Kotwali 8 97 31988 - - - Lalbagh* 11 119 57248 2 4 75 Mirpur 10 87 113353 - - - Mohammadpur* 7 48 57551 2 4 61 Sutrapur* 11 81 49286 2 4 61 Subtotal (BRA) 47 432 309426 6 12 197 Cantonment 2 19 29761 - - - Demra 5 23 52444 - - - Dhanmondi* 4 30 33451 2 5 42
5 The DCC, an autonomous local government body under the Ministry of Local Government, Rural Development and Cooperatives, is run by an elected Mayor and 90 elected Ward Commissioners (one Commissioner for each Ward). 6 A thana is a type of sub-district. The whole country is divided into 64 districts (called zila). Each district is divided into several thanas. To avoid confusion, it should be mentioned that a police station is also known as ‘thana’ in Bangladesh.
7 The third Population Census was conducted in 1991 and the fourth in January 2001. During the present survey and data collection, the results of the 2001 census had not been published. That is why for the sampling frame, the 1991 population statistics are used. However, for aggregation purposes, population data of preliminary results from the 2001 Census, released by BBS in August, 2001, are used.
Gulshan* 5 39 38048 2 4 53 Motijheel 6 35 36059 - - - Ramna * 5 27 30851 2 4 42 Sabujbagh* 9 30 55919 2 4 66 Tejgaon 4 20 37644 - - - Uttara 3 4 19413 - - - Subtotal (OBA) 43 227 333590 8 17 203 Total (DCC) 90 659 643016 14 29 400
Notes: * indicates selected for the survey
DCC: Dhaka City Corporation, BRA: Buriganga River area, and OBA: Outside Buriganga River area.
Source: Own compilation. Population data is adopted from BBS (1993).
Another difficulty in identifying a household is that in many cases more than one household may live in one unit or even in one room. All these issues posed a problem in establishing a reliable and representative sampling frame. Under these circumstances, it was decided to construct a sampling frame for this survey using the following methods.
Stratifying the Population: To make sure that the samples were representative of the population, a stratified simple random sampling technique, based upon Czaja and Blair (1996), Sarantakos (1998) and Kumar (1999), was employed to select a sample of 400 households (see Table 4.2). Besides ensuring representative sampling, the purpose of stratification was to examine any variation between people living near the Buriganga River and those living at a greater distance9 with regard to various attitude-behaviour attributes.
From the start of the design of the sampling frame, the whole study area (i.e. Dhaka City) was stratified into two constituents: ‘Buriganga River area (BRA)’ (i.e. boarding on the river) and ‘outside Buriganga River area (OBA)’. This division roughly corresponds to the demarcation of ‘old Dhaka’ and ‘new Dhaka’10. Accordingly, five thanas fell within the Buriganga River area (BRA), and nine thanas fell outside. Three thanas from BRA and four thanas from OBA were selected randomly for the survey. The sample of 400 households was then drawn from these seven thanas in proportion to each
9 Stratification also satisfies the probability sampling criterion, i.e. each and every member (household) has an equal chance of being selected.
10Some adjustments were required to justify this demarcation. As distance is the basis of this demarcation (BRA is defined as within one km from the Buriganga River), one mohalla (Lalmatia) of Mohammadpur thana was found to be more than one km distant from the Buriganga River although it belonged to BRA and another mohalla (Hazaribagh) of Dhanmondi thana was found within one km distance from the Buriganga River. These two mohallas were swapped
thana’s population, resulting in 42-75 households being assigned to each thana (see Table 4.2). Then from each thana, two wards were selected and from each ward two mohallas were chosen. These resulted in 14 wards, 29 mohallas11 and 400 households (197 households from the Buriganga area and 203 households from outside the Buriganga). All these selections were based on a random procedure. Further details of the selected thanas, wards and mohallas are provided in Appendix II.
Household Selection: After selecting a mohalla, trained enumerators12 were sent to that mohalla. At first, they observed the physical location of the mohalla. Then they started listing the households from the north-west corner of the mohalla (for sampling frame, see Appendix III). They listed all existing households in the mohalla starting from the right hand side and moving to the left hand side of each street. After finishing the listing of households, they started the interview process. Among the listed households, every 20th household was selected and interviewed to ensure that the samples were random. In a selected household, if nobody was found or answered the door for the house visited, or the person needed for the interview was not available, interviewers were required to re-visit the household two more times on a different day. In the case that the household was still non-contactable, residences located before and after that household respectively were used as a ‘replacement sample’.
Respondent Selection: Selecting a household was not the end of the sample selection procedure. After selecting a household, the task was to identify a participant from that particular household. For that purpose a ‘contact sheet’ was developed (see Appendix
IV). The interviewer first sought permission of the contact person (i.e. the person who answers the door) to randomly select a participant from the members of the household to participate in the survey. To do this, all the eligible members13 were listed by their nickname14 and gender, then a participant was selected using the ‘random number table’
11 From ward 20 of Dhanmondi thana, one additional mohalla (Science Laboratory) was required to be selected to complete the 42 households because of the inadequate number of households in the two selected mohallas (Dhaka College and Elephant Road). This resulted in there being three mohallas in ward 20.
12The training process is discussed later in this chapter.
13 Two criteria were used for eligibility of a participant for being selected, i.e. (i) 18 or above years of age, and (ii) mentally and physically fit. Servants, caretakers and security guards were excluded from the survey. Although they, particularly servants, live with the household and share the same food, they were excluded from the sample frame for several reasons. These are: (i) they appeared extremely shy or reluctant to express their opinion in the presence of any family member; (ii) they were not allowed to be interviewed in many instances; and (iii) due to custom/culture, many did not recognize them as members of household.
14Due to cultural practices, in some instances, the contact person (particularly in the case of conservative women)
designed for the survey (see Appendix V). If it was the contact person who was the selected respondent then the interview was started if she/he agreed or an appointment was made for another time. If the respondent was other than the contact person, then either the interview was started or an appointment was made for another time. All the interactions were in Bengali, the local language.