Figure 3: A typical adaptive sequencing trial design5

The choice of the study design depends on:

  • state of knowledge about the problem;
  • nature of the problem and its environment;
  • type of objectives;
  • available resources;
  • ingenuity and creativity of research team.
Table 1: Factors dictating the most appropriate choice of study design
State of knowledge of the problem Type of research question Appropriate study design
Knowing that a problem exists, but little understanding of its characteristics or possible causes.
  • What is the nature/magnitude of the problem?
  • Who is affected?
  • How do the affected people behave?
  • What do they know, believe and/or think about the problem and its causes?

Descriptive studies:

  • Cross-sectional surveys.
Suspecting that certain factors contribute to the problem.
  • Are certain factors indeed associated with the problem? (e.g. lack of pre-school education related to low school performance? Is a low fibre diet related to carcinoma of the large intestine?)

Analytical (comparative) studies:

  • Cross-sectional comparative studies.
  • Cohort studies.
Having established that certain factors are associated with the problem: establishing the extent to which a particular factor causes or contributes to the problem.
  • What is the cause of the problem?
  • Will the removal of a particular factor prevent or reduce the problem? (e.g. stopping smoking, providing safe water)
  • Cohort studies.
  • Experimental or quasi-experimental studies.
Having sufficient knowledge about cause(s) to develop and assess an intervention that would prevent, control or solve the problem.
  • What is the effect of the particular intervention/strategy? (e.g. treating with a particular drug; being exposed to a certain type of health education).
  • Which of two alternate strategies gives better results? Which strategy is most cost-effective?
  • Experimental/ or quasi-experimental studies.
Example

A mixed methods protocol to evaluate the effect and cost-effectiveness of an integrated electronic diagnosis approach (IeDA) for the management of childhood illnesses at primary health facilities in Burkina Faso.7

Background: Burkina Faso introduced the Integrated Management of Childhood Illnesses (IMCI) strategy in 2003. However, an evaluation conducted in 2013 found that only 28% of children were assessed for three danger signs as recommended by IMCI, and only 15% of children were correctly classified. About 30% of children were correctly prescribed with an antibiotic for suspected pneumonia or oral rehydration salts (ORS) for diarrhoea, and 40% were correctly referred. Recent advances in information and communication technologies (ICT) and the use of electronic clinical protocols hold the potential to transform health care delivery in low-income countries. However, no evidence is available on the effect of ICT on adherence to IMCI. A mixed methods study that aims to measure the effect of the IeDA innovation (an electronic IMCI protocol provided to nurses) is planned in two regions of Burkina Faso.

The study focuses on three key questions: (i) How does the effectiveness and the cost of the intervention vary by type of health worker and type of health centre? (ii) What is the impact of changes in the content, coverage and quality of the IeDA intervention on adherence and cost-effectiveness? (iii) What mechanisms of change (including costs) might explain the relationship between the IeDA intervention and adherence? In order to answer these questions, the study combines the following mixed methods: stepped-wedge trial, a realistic evaluation and an economic study in order to capture the effect of the innovation after its introduction on the level of adherence, cost and acceptability.