1.8 Summary

Studies may be observational or experimental. Observational studies can usually be classified as retrospective, prospective, or cross-sectional. Experimental studies can usually be classified as true experiments or quasi-experiments. Cause-and-effect conclusions can only be made from well-designed true experiments. Ideally studies should be designed to be internally and externally valid.

The following short videos may help explain some of these concepts:

---

This material was written by Peter K. Dunn and adapted by Amanda J. Shaker. Unless otherwise stated, material within this work is licensed under a Creative Commons Attribution-Non Commercial-Share Alike License CC BY-NC-SA