The following is an idealized experimental episode which is based on Rao et al. (2009). You are to read the background, experimental setup, and results, and then do the proper quantitative analysis.
The learning outcomes associated with this assignment are:
1) Differentiate experimental design: Using the information provided, figure out if the experiment is a randomized experimental design, prospective design, or retrospective design.
2) Differentiate the hypothesis: Using the information provided, figure out the dependent and independent variable and the relation between the two.
3) Analyze quantitative data using statistical analysis. You are expected to master the concepts of sample sizes, confidence intervals, margin of error, and correlation interval.
The Study
Background:
Recently it was discovered that gut pathogens in the GI tract can communicate with the central nervous system and influence behavior associated with emotion, anxiety
in particular, even at extremely low levels and in the absence of an immune response [Lyte et al. 1998, Goehler et al. 2007]. Researchers have also shown that the administration of certain bacteria found in soil may support resilience and positively alter stress-related emotional behavior in animals under experimental stress [Lowery et al. 2007)].
The Experimental Setup:
Patients who met all inclusion/exclusion criteria were evaluated using the Beck Depression Inventory (BDI) and the Beck Anxiety Inventory (BAI). Patients also provided stool samples, taken over 3 days, at the evaluation phase. Kits were provided to the patients according to guidelines of appropriate collection as per the University of Toronto, School of Medicine, Department of Nutritional Sciences. Samples were sent to the Fecal Laboratory of the University of Toronto, Department of Nutrition for evaluation. Using culture technique, the stool samples were assessed for total aerobe, anaerobe, Lactobacillus spp, and Bifidobacteria spp counts.
After collection of the data and samples at the initial evaluation phase, CFS patients were randomized to begin an intervention phase, an eight-week period where each patient consumed either a specific lactic acid probiotic bacteria or placebo by mouth. The groups were balanced equally in terms of members. After each main meal, or three times daily, patients consumed the contents of an unmarked sachet containing 8 billion colony forming units (cfu) of Lactobacillus casei strain Shirota (LcS) or a placebo with identical taste and appearance. Each CFS patient in the active intervention group consumed a total of 24 billion cfu of LcS probiotic per day. Follow-up evaluation phase: After 8 weeks of intervention, LcS or placebo, subjects were re-evaluated by completion of the BDI and BAI, and a second stool analysis was conducted using the same collection and culture methods.
1. What kind of study is this? Evaluate the study in terms of effectiveness of design. Is the design good? Why or why not? Be as specific as possible.
2. What is the experimental hypothesis? Be as direct as possible.
3. Is this hypothesis statistically significant, given the results of the study? Show your quantitative work. What are the highs and lows of the intervals (i.e. what is the greatest difference and what is the least difference?). Here, you’ll have to see if there’s overlap or not to make a conclusion about significance.