Assessment of the validity and reliability of the survey

Validity

Validity is whether one actually measures what one intends to measure (Coggon, et al., 2003). A study is considered to be valid if the findings can be taken as being a reasonable representation of the true situation (Margetts & Nelson, 1997). In this case this means whether the mothers’ actual infant feeding practices were measured. The questions about the mothers’ infant feeding practices should ideally have been tested or validated (Kunnskapssenteret, 2008). Some of the questions on infant feeding were used in a pre-tested, structured questionnaire used in a cross-sectional survey in Tanzania from 1999 which was part of Marina M. de Paoli’s Doctor of Philosophy [PhD] (de Paoli, 2004). All the questions were however not pre-tested.

There are different aspects of validity (Ringdal, 2007). One is called face validity which concerns whether the questions about infant feeding really covers the aspects of interest in the term “infant feeding practices”. In the survey from 2007 questions about infant feeding practices involved how the infants had been fed, what advice the mothers had been given and the mothers’ knowledge about MTCT and infant feeding. Another aspect of validity is content validity where

the use of term is essential (Ringdal, 2007). Related to the term “infant feeding practices”, the content validity refers to the degree to which the aspects of interest are covered through the questions in the questionnaire. The WHO assessment tool from 2001 was presented in Table 15 to give a description of questions that could have been useful for describing the mothers’ infant feeding practices.

External validity refers to the way results of a study sample can be generalized to apply the study population (Ringdal, 2007). As described in section 6.1.1 the findings in this master thesis can most likely not be generalized to apply to all mothers with or without HIV in Khayelitsha in 2007. To be externally validated a study must be internally valid (Margetts & Nelson, 1997). The assessment of the validity of the measures used in the study and the conduct of the study are often referred to as the internal validity (Margetts & Nelson, 1997). High internal validity requires good control of possible bias in the way the data is collected, analysed and interpreted (section 6.1.3) (Margetts & Nelson, 1997).

Reliability

High reliability is a prerequisite for high validity. Reliability is whether repeated measurements with the same measuring instrument give the same result (Ringdal, 2007). In this master thesis the main measuring instrument was the questionnaire used in the cross-sectional survey from 2007. There are several ways to assess the reliability of data (Ringdal, 2007). One is based on general criticism of the data. Since this master thesis was based on data that was already collected it was important to understand how the data had been collected. It was then necessary to look closely and carefully at how the questions about infant feeding and other relevant questions had been formulated to discover and reveal possible biases. A comparison with the assessment tool from WHO, was done for this purpose. Though many of the questions in the questionnaire were relevant for the topic of this master thesis, mistakes and weaknesses with some of the questions were found. Table 16 presents some examples of suggestions to improved question formulations. The time-intervals in questions O.3 through O.6 overlapped and this could have led to misunderstandings. Still the answers to these questions were interpreted based on the suggested improved formulations in Table 16 when presenting the findings. There were several weaknesses in the formulation of the questions on what food the mothers regarded as best for small children. The questions did for instance not directly say anything about the mothers’ knowledge about

MTCT and infant feeding. The questions were furthermore formulated in such a way that the mothers could give the same answer to every question. It was thus not paid much attention to these questions in the analysis.

Table 16: Suggestions to improved question formulations in the questionnaire

Questions in the questionnaire used in the 2007 survey Suggestions to improved question formulations Questions O.3 - O.6

How did you or your partner feed your last born child? The first month

The first 1-3 months The first 3-6 months The first 6-12 months

How did you or your partner feed your last born child? (according to his/her age)

Age 0-1 month Age 2-3 months Age 4-6 months Age 7-12 months Question O.1.1 (- O.1.6)

In general, cow’s milk is the best (food) for a small child. (0-6 months).

- Strongly disagree - Disagree

- Neither agree nor disagree - Agree

- Strongly agree - Don’t know

In general, what is the best food for a small child the first 0-6 months?

OR

In general, what is the best and worst food for a small child the first 0-6 months on a scale from 1 to four (where 1 being best and 4 worse)?

- Cow’s milk - Breast milk

- Infant feeding formula - Mixed feeding - Don’t know Question O.2

When you were pregnant and went for check-up, what infant feeding advice were you given?

When you were pregnant with your last born child and went for check-up, what infant feeding advice were you given?

Follow-up questions:

- Who gave you the advice?

- What age of the child was the advice referring to?

- Were you HIV-positive at that time?

The quality of the data and the data analyses affects the reliability (Ringdal, 2007). It was thus important to look at the accuracy in the registration of the data and search for errors and correct these. Another way to assess reliability is by using the so called test-retest-technique. This technique is about measuring the degree of correlation between two repeated measurements of the same variable (Ringdal, 2007). A test-retest technique was not done after the survey in 2007.