Distinguishing study designs

Course activity

STAT218

Recall that the difference between an observational study and an experiment hinges on whether researchers intentionally intervene on the system of study (experiment) or passively record outcomes (observational study).

In this activity you’ll read abstracts from a few published studies and determine what kind of study is described in the abstract. You do not need to consider the examples in order — start with the ones that look most interesting.

For each example, identify the following:

Example 1: selenium exposure and Mediterranean diet

The following is from the abstract of a study investigating dietary mitigation of selenium exposure:

Selenium is a trace element found in many chemical forms. Selenium and its species have nutritional and toxicologic properties, some of which may play a role in the etiology of neurological disease. We hypothesized that adherence to the Mediterranean-Dietary Approach to Stop Hypertension Intervention for Neurodegenerative Delay (MIND) diet could influence intake and endogenous concentrations of selenium and selenium species, thus contributing to the beneficial effects of this dietary pattern. We carried out a cross-sectional study of 137 non-smoking blood donors (75 females and 62 males) from the Reggio Emilia province, Northern Italy. We assessed MIND diet adherence using a semiquantitative food frequency questionnaire. We assessed selenium exposure through dietary intake and measurement of urinary and serum concentrations, including speciation of selenium compound in serum … Adherence to the MIND diet was positively associated with dietary selenium intake and urinary selenium excretion, whereas it was inversely associated with serum concentrations of overall selenium and organic selenium … Our results suggest that greater adherence to the MIND diet is non-linearly associated with lower circulating concentrations of selenium and of 2 potentially neurotoxic species of this element, selenoprotein P and selenate. This may explain why adherence to the MIND dietary pattern may reduce cognitive decline.

Urbano, T., et al. (2023). Adherence to the Mediterranean-DASH Intervention for Neurodegenerative Delay (MIND) diet and exposure to selenium species: A cross-sectional study. Nutrition Research.

Example 2: fermented kimchi and glucose metabolism

The following is from an abstract of a study investigating possible benefits of kimchi consumption among prediabetic individuals:

With the increased incidence of diabetes mellitus, the importance of early intervention in prediabetes has been emphasized … We hypothesized that kimchi and its fermented form would have beneficial effects on glucose metabolism in patients with prediabetes. A total of 21 participants with prediabetes were enrolled. During the first 8 weeks, they consumed either fresh (1-day-old) or fermented (10-day-old) kimchi. After a 4-week washout period, they switched to the other type of kimchi for the next 8 weeks. Consumption of both types of kimchi significantly decreased body weight, body mass index, and waist circumference. Fermented kimchi decreased insulin resistance, and increased insulin sensitivity … Systolic and diastolic blood pressure (BP) decreased significantly in the fermented kimchi group. The percentages of participants who showed improved glucose tolerance were 9.5 and 33.3% in the fresh and fermented kimchi groups, respectively.

An, S. Y., et al. (2013). Beneficial effects of fresh and fermented kimchi in prediabetic individuals. Annals of Nutrition and Metabolism, 63(1-2), 111-119.