Research designs represent different models or strategies  for collecting, analyzing, interpreting and reporting data in research studies. They include;  Surveys, Experiments, Case studies, Grounded theory, Action research ,the various Mixed methods research designs, Ethnography,  Discourse analysis ,Evaluation research, Appreciative enquiry e.t.c.

Longitudinal or cross-sectional studies are Time horizons -the time-scale approaches you adopt in doing research.If these are short-term where the study adopts a  ‘snapshot’ approach in which  the data are collected at one point in time ,then the Time horizons are cross-sectional. On the other hand ,if the study treks the research problem over an extended period of time, then the Time horizons are Longitudinal.

Research designs represent different models or strategies  for collecting, analyzing, interpreting and reporting data in research studies. They include;  Surveys, Experiments, Case studies, Grounded theory, Action research ,the various Mixed methods research designs, Ethnography,  Discourse analysis ,Evaluation research, Appreciative enquiry e.t.c.

Longitudinal or cross-sectional studies are Time horizons -the time-scale approaches you adopt in doing research.If these are short-term where the study adopts a  ‘snapshot’ approach in which  the data are collected at one point in time ,then the Time horizons are cross-sectional. On the other hand ,if the study treks the research problem over an extended period of time, then the Time horizons are Longitudinal.

@Lysias "If I get you right, it means "cross-sectional design" is not a research design on its own, but a 'time horizon -a time-scale approach adopted in doing research" right?

That is exactly my point.

Thanx

According to Sekaran (2003) a research design is set up to decide on, among other issues, how to collect further data, analyze and interpret them, and finally, to provide an answer to the problem.

 Sekaran (2003) has identified six elements of research design. They are listed below.

1.      Purpose of the study

2.      Type of investigation

3.      Extent of researcher interference

4.      Study setting

5.      Unit of analysis

6.      The time horizon

Sekaran (2003) wrote:

“The researcher would determine the appropriate decisions to be made in the study design based on the problem definition, the research objectives, the extent of rigor desired, and cost considerations. Sometimes, because of the time and costs involved, a researcher might be constrained to settle for less than the ideal research design. For instance, the researcher might have to conduct a cross-sectional instead of a longitudinal study, do a field study rather than an experimental design, choose a smaller rather than a larger sample size, and so on, thus sub-optimizing the research design decisions and settling for a lower level of scientific rigor because of resource constraints."

According to Sekaran (2003) time horizon of study can be either cross-sectional or longitudinal. 

For more details please read Sekaran's book.

Reference

 Sekaran, U., 2003. Research methods for business: A skill building approach. John Wiley & Sons.

Thank you Iddagoda. Most useful. I'd get the paper and read.