Yes, you can use cross-sectional studies in a systematic review, depending on the research question you are addressing and the inclusion criteria you set for your review. Cross-sectional studies are observational studies that collect data from a population at a single point in time. They are used to assess your prevalence directly. In systematic review, what you need is the evidence based studies, not type of studies at most. So any relevant and credible studies can be included.

Yes, definitely.

It is possible to include cross-sectional studies in a systematic review.

This is because although a systematic review usually includes only randomized controlled trials (RCT) for its subsequent analysis (which can either be a meta-analysis or a narrative synthesis), it is also possible for a systematic review to include a non-randomized controlled trial (i.e. non-RCT) such as a cross-sectional study for its subsequent analysis.

A systematic review will usually also include a meta-analysis. However, if the degree of heterogeneity among the included studies is too high, then it is recommended to skip meta-analysis and proceed with a narrative synthesis instead.

The QUORUM statement is a reporting checklist for a systematic review which includes a meta-analysis of randomized controlled trials (RCT), while the MOOSE statement is a reporting checklist for a systematic review which includes a meta-analysis of observational studies (which are non-RCT).

Finally, AMSTAR is used to evaluate the methodologic quality of systematic reviews and meta-analyses of randomized controlled trials.

However, AMSTAR2 will be preferred for the evaluation of methodologic quality of systematic reviews and meta-analyses of RCT and non-RCT (such as cross-sectional studies, etc.).

Having a majority of cross-sectional studies in your mixed methods systematic review does not necessarily invalidate your dissertation. Cross-sectional studies, while not technically primary data in the sense of data collected specifically for your research, are still valuable sources of information in systematic reviews.

In a mixed methods systematic review, you aim to synthesize evidence from various types of studies, such as qualitative, quantitative, and mixed methods research, to address your research questions comprehensively. While primary data collection is one aspect of mixed methods research, the synthesis of existing data from published studies is another valid approach.

Cross-sectional studies can provide valuable insights into the prevalence, distribution, and associations of variables of interest at a specific point in time. They can contribute to the overall understanding of a research topic and help identify patterns or trends that may inform future research or practice.

To clear up the confusion. Cross-sectional studies are primary data (in most cases).

Primary data is data that is collected by the researchers themshelves, secondary data is collected by someone else.