Review article: The author(s) provide an extensive review of the scientific literature available on the topic. The most significant studies to date are described, including their limitations, and a summary of the current state of knowledge on this topic is included. The list of studies cited is usually very long. This type of article is an excellent starting point to become familiar with background and current scientific knowledge on a specific topic. If the article was written recently, the list of references may be a good place to start in locating published studies relevant to the topic.
Example Review Article: Kennaway, D. J. (2015). Potential safety issues in the use of the hormone melatonin in paediatrics. Journal of paediatrics and child health, 51(6), 584-589. Article Full Text
- Systematic Review articles are a specific type of review article where the authors follow a prescribed protocol to conduct a review of evidence to answer a specific research question or questions. Following a comprehensive literature search (often including hundreds or thousands of initial results), articles for review are selected based on pre-designed eligibility criteria. Finally, all included articles are reviewed and synthesized results are provided for outcomes, data, and other information that addresses the research question or questions. *Some Systematic Reviews include a ‘Meta-Analysis’ of data from some or all included articles. See below for a full description of a Meta-Analysis article.
Example Systematic Review Article: Barrett, J. R., Tracy, D. K., & Giaroli, G. (2013). To sleep or not to sleep: a systematic review of the literature of pharmacological treatments of insomnia in children and adolescents with attention-deficit/hyperactivity disorder. Journal of child and adolescent psychopharmacology, 23(10), 640-647. Article Full Text
Clinical Trial/Intervention: The investigators tested an intervention or treatment by giving one group of subjects the treatment and comparing results for that group with results in a control or comparison group that did not get the treatment.
Example Clinical Trial Article: Cortesi, F., Giannotti, F., Sebastiani, T., Panunzi, S., & Valente, D. (2012). Controlled‐release melatonin, singly and combined with cognitive behavioural therapy, for persistent insomnia in children with autism spectrum disorders: a randomized placebo‐controlled trial. Journal of sleep research, 21(6), 700-709. Article Full Text
Observational (could be cross-sectional or longitudinal): The investigators just watched what occurred naturally, without interfering or giving any intervention or treatment. Typically, different subgroups of the subjects are compared with each other (i.e. men and women, young and old, low or high nutrient status for a particular nutrient, low or high intake of something, such as folic acid, alcohol, omega-3 FAs, etc.). Cross-sectional studies collect data during one time period only, while longitudinal means that the subjects are followed over a period of time with multiple data collection points.
Example Observational Article: Jan, J. E., Ribary, U., Wong, P. K., Reiter, R. J., Bax, M. C., & Wasdell, M. B. (2011). Cerebral modulation of circadian sleep-wake rhythms. Journal of Clinical Neurophysiology, 28(2), 165-169. Article Full Text
Meta-analysis: The investigators take the results from several similar studies on the same topic and conduct statistical analysis on the data combined from all of the studies. This gives a bigger sample size and allows for more powerful analysis which helps determine whether a particular factor truly has significant effects.
Example Meta-Analysis Article: Ferracioli-Oda, E., Qawasmi, A., & Bloch, M. H. (2013). Meta-analysis: melatonin for the treatment of primary sleep disorders. PloS one, 8(5), e63773. Article Full Text