Monthly household income: This group of variable was divided into seven groups. 1 was coded as those that their monthly household income is equal to or less than 1999 dalasis. 2 was coded as those that monthly income range from 2000 to 4000 dalasis, 3 was from 5000 to 70000 dalasis, 4 was from 8000 to 10000, 5 was from 11000 to 13000, 6 was from 14000 to 16000 dalasis and 7 was coded as greater or equal to 17000 dalasis. All the money was express in Gambian currency, dalasi.
Monthly household expenditure: Monthly household expenditure was a continuous variable during the study but was later converted to categorical variable. For the categorical variable of the monthly household income, it was divide into five groups.1 was coded as less than 1000dalasis, 2 was coded as 1000dalasis to 5999dalasis, 3 was coded as 6000dalasis to 10999dalasis, 4 was coded as 11000dalasis to 15999dalasis and 5 was coded as greater than or equal to 16000dalasis.Again all the money were express in Gambian currency (GMD).
Last medical expenditure: Last medical expenditure was also a continuous variable during the study but was later converted to categorical variables. It was divided into five groups where 1 was coded as less than 300dalasis, 2 was coded as 300dalasis to 599dalasis, 3 was coded as 600dalasis to 1999dalasis, 4 was coded as 2000dalasis to 2999dalasis and 5 was coded as equal to or greater than 3000dalasis.
Number of Household size: Household size was a continuous variable but was converted into categorical variables during the analysis process. It was divided into four groups. 1 was coded as
household size between 1 and 3, 2 was coded as between 4 and 6, and 3 was coded as between 7 and 9 and 4 was coded between 10 and 12.
Number of Household children aged less than 6: Household children size that are less than six years old in the family were also collected as a continuous data but was converted as a categorical during the analysis process. It was divided into four groups. 1 was coded as household that do not have children less than 6, 2 was coded as household that has only one child less than 6 years old, 3 was coded as household that has two children that are less than 6 years old and 4 was coded as household that has three children that are less than 6 years old.
Number of Household female size: This is the number of females in the family. The number of females in the family was divided into four groups. 1 was coded as household female size between 1 and 3, 2 was coded as household female size between 4 and 6, 3 was coded as household female size between 7 to 9 and 4 was coded as household female size between 10 to 12.
Duration of stay in their Homes: This is the number of years the respondent live in their place. It was a continuous variable but was converted to categorical variable during the analysis process. It was divided into four groups in which 1 was coded as less or equals to 20 years of stay in a place, 2 was coded as 21 years to 30 years of stay in a place, 3 was coded as 31 years to 40 years of stay in a place and 4 was coded as 41 years to 50 years of stay in a place.
Medical History Variable
Previous experience of malaria: This is the number of times the respondent have malaria in the year.
1 was coded as once in a year, 2 were twice in a year, 3 were thrice in a year and 4 were fourth times in a year.
Table 3.1 Operational definitions of dependent and independent variables
Variable Definition Nature of the Variable
Dependent Variable Willingness to pay (WTP) log_wtp
Willingness to pay for the Household head, wife and children. The amount is in Dalasis(GMD) Education Lower than elementary school=1, elementary
school=2, junior high school=3, senior high
3.4 Study Design and Subjects
Willingness to pay (WTP) is a common method to estimate monetary values for health care interventions. WTP is also known as contingent evaluation. In the WTP approach, the maximum amount that an individual is willing to pay to obtain a good is elicited using a bidding game method.
The bidding game present the respondent with an amount and ask whether she is willing to pay that amount. Depending on the answer given, respondent are asked to bid up or down using the options in the questionnaire until the maximum number is reached. The WTP technique was original developed by an environmental economists, but is increasingly used in health economics (Grutters et al, 2009).
The preference of the study population was determined by a bidding game, a widely accepted method for accessing consumer stated preferences (as opposed to revealed preferences through expressing demand at given process), in the absence of a market for a product. Bidding games produce reliable results even in illiterate populations (Sauerborn et al., 2005).
In this study, a structured willingness to pay (WTP) questionnaire was administered to those already diagnosed malaria patients and household head throughout the survey.
This study will help government, researchers and funding agencies with the basis for intervening in the market and setting priorities in malaria vaccines. Such strategies might include subsidizing payments, targeted subsidies or providing free drugs to the poor.
The exclusion criteria were household head above 50 years of age were not interview. The inclusion criteria was to seek the respondent consent first before interviewing them and also it was only already adult diagnosed malaria patients were interview at the Royal Victoria teaching Hospital (RVTH) in
Banjul which is the main referral hospital in The Gambia. Adult household heads in the community were also interviewed in their compounds and also in work places.
They were interviewed by a trained interviewer in September 2010 while waiting for their malaria drugs at the outpatient clinic at RVTH.
A questionnaire was designed to elicit respondent WTP for a hypothetical malaria vaccine in The Gambia capable of preventing maternal malaria and childhood malaria.
One hundred already diagnose malaria patients were given the questionnaire to fill out and one hundred household head were also given the questionnaire to fill. However, the household heads and the patients were asked their willingness to pay for their spouse and their children. If the respondent is a woman, she is also equally asked their willingness to pay for their husband and children.
Willingness to pay for the vaccines were elicited by a bidding method in which respondent being asked how much they would be willing to pay for the vaccine against maternal malaria and childhood malaria by giving them the first bidding amount which is 1000 dalasis.
If the respondent‟s answer to the first bid offered which is 1000, the interviewer then increases the bid to 25% and asked the same question again. If the respondent still wants to bid more than the amount then the amount is increase to 25% until they reach at the last bidding amount.
However, if the respondent rejects the initial bid, the intervierver decreases the amount to 25%. If the respondent still rejects the amount, then the bidding is then reduced again by 25%. This continued until the respondent reached its least bidding amount for the vaccine.