Generally a longitudinal study would follow a cohort over a certain time period. If n=1,  your study becomes a longitudinal case study. Then you have double constraints, those of a case study and those of a longitudinal study. I can imagine constellations where a longitudinal case study is indicated. Be explicit about the motives of your methodological choice.

Generally a longitudinal study would follow a cohort over a certain time period. If n=1,  your study becomes a longitudinal case study. Then you have double constraints, those of a case study and those of a longitudinal study. I can imagine constellations where a longitudinal case study is indicated. Be explicit about the motives of your methodological choice.

Longitudinal can be a quantitative study where as case study is qualitative

Charles and Aminuddin, Thank you so much. 

Then, Can I call it longitudinal case studies (even if the research period is three months)?

The condition is not the duration, but your observations/measures/interviews (data) must come from different (at least two) moments in time. Reconstructing the evolution in time can not be based on participants' report. Then it would be a narrative study. I do not see the dichotomy between quantitative and qualitative study as dramatic as Aminuddin does.

I agree with Charles concerning case study. Both within qualitative and quantitative research can use case study for their research questions. Case study is a study where you have a few participants, in some cases only one participant, insome cases more. Polit and Beck gives the following definition: "A research method that involves a thorough, in-depth analysis of an individual, group, institution or other social unit."

Polit, D. F., & Beck, C. T. (2012). Nursing research: generating and assessing evidence for nursing practice. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins.

A longitudinal study is as described by Charles, a study following participants over time. The authors mentioned above gives this definition: " A study designed to collect data at more than one point in time"

Often this means that the time points when you collect your data are pre-defined and the same for all participants i.e data is collected at a certain ocassion like when somethings happen, and then at certain time points after that. It could be at the time of a babys birth and each month after that until the baby is one year, or when a person is diagnosed with a disease and every year after that, or when someone gets their exam, and every sixth month after that to follow ther progress as newly graduated.

I do not think I would use any of those words to label the method you indicate you are using.

Best regards

Åsa

Thank Charles and Åsa so much. This is very helpful and I really appreciate your support. 

I think some difficulty may come into play if the participants in the diary component of the study complete diaries on greatly different numbers of occasions. Does a diary omission mean that you lost the recording of a key event or was it because the participant was so busy at work or family matters that day that he or she could not complete the diary and the key event did not occur? I don't know what your study is about but there may be a way to structure data collection so that each participant has a chance to complete the diary once a day or once a week or every Sunday and Wednesday. 

It may also be helpful to include both qualitative data and quantitative data that are amenable to statistical analyses in the same diary.

Case study is a detailed investigation of a person, group, or phenomenon. It is "bounded" by definition, place, time, and activity (Baxter & Jack, 2008). Boundaries of a case are set in order to facilitate a reasonable study.

Thank Mr. Irvin and Miss. Nyasha. It seems that I was confused between the longitudinal studies and case studies, but now it becomes clear that there is no overlap between these concepts. Case studies is a way of data collection (a method) while the longitudinal studies deal with time for the data collection or it can be a way to measure one thing over and over again. Therefore, in my own situation, it might be called longitudinal study because I would look for the individual over and over again.

Thank you all of you for your time and your knowledge. 

Very welcome, Omar. I would just add that you could conduct a longitudinal case study, as long as you articulate your multiple data collection points and you specify the time. But, as you pointed out, a must of case study is that it includes multiple forms of data.