Medicine and public health have relied on peer-reviewed published scientific literature to help guide progress in patient treatment and public health interventions for decades- even centuries. For example, when we did the fact-finding to inform our decision about whether to add the petitioned conditions to the list of disorders that qualify for AZ medical marijuana cards- we (and the UA) turned to the scientific literature. Within the scientific literature- there are different categories of research designs that each have their strengths and weaknesses.
Studies to assess the effectiveness of an intervention (like whether Cannabis is an effective treatment for depression) can have an Experimental or Observational design. For example, a randomized and controlled experimental study selects participants at random and places them in the intervention or control group and then follows up on the subjects over time to assess any differences in outcomes. Experimental studies generally provide the highest quality and most reliable results.
An Observational study isn’t really experimental- rather, it’s a study that looks at natural variation regarding an intervention (or exposure) and looks at differences in outcomes among people or populations. Controlled observational studies can look at before and after conditions. For example, a cohort observational study can look at populations prospectively, retrospectively, or as part of a time series. Observational studies can also be of case-control or cross-sectional design. Observational studies can also simply look at a series of cases and look at interventions and outcomes without a control group.
In general, the highest quality studies use the experimental approach and include a randomized design. Studies in the category can be very high quality if there is little bias and confounders are identified and controlled for… and if the study is large. Observational studies are generally of lower quality- although they can be quite useful if they limit bias, are consistent, direct, and control for confounding factors. The lowest quality study is what’s called a case series with no controls. Often, case series studies are simply observations made by clinicians- but without control groups… and they usually don’t control for confounders or bias.
Anyway- you get the idea… scientific studies are absolutely critical to helping the public health system design interventions, make policy decisions, and measure results. Published scientific literature allows us to use science to inform our policy decisions and interventions in an objective way- increasing the likelihood that the public health system makes a positive impact in people’s lives. Understanding what makes a published scientific study strong and compelling is critical to sorting through the published scientific literature for the types of strong studies that make for solid foundations for policy and intervention decisions.
My post tomorrow will summarize ways to evaluate the quality and reliability of various kinds of studies.