Which of the following are included in major research designs ? Choose the correct answer from the options given below :

Experimental, cross-sectional, longitudinal and case-study designs all count among the major research designs.

Restricting the answer to experimental and case-study alone drops two equally major designs.

Limiting it to cross-sectional and longitudinal ignores the experimental and case-study forms.

Leaving out the longitudinal design in the three-part option is unjustified.

Bryman also lists comparative design as a fifth major type alongside these four.

The choice of design flexes to fit the research question, resources and time available.