Journal Club- Basic Stats: Cardiovascular Effects of Intensive Lifestyle Intervention in Type 2 Diabetes

I decided to start a new feature that hopefully you and I will find useful. It will only be useful if you work thru the questions and have a dialogue thru the comments section.

My plan is to post a different article about once a month and have questions for you to answer. 1 week later (or so) I will then either post a video review of my answers or just write about the answers. I plan to focus mostly on the basics but at times I will cover advanced topics also as “extra credit”. I am mostly going to parallel the journal club curriculum we are using this year at UAB. I welcome comments to make this better or articles you want to read.

58 yo M with DM-2, hyperlipidemia and HTN presents to you for a follow-up visit. He takes metformin 1000mg BID, lisinopril 20mg daily, and pravastatin 40mg nightly. His most recent HgA1C was 6.9% and LDL was 88 mg/dl. In the office his blood pressure is 128/67 mm Hg and BMI is 32. You counsel him to lose weight and he responds “My blood pressure, cholesteol and A1C are good. How is losing weight going to help my heart?” What do you tell him?

After reading the statistical analysis section (pgs 147-148) of the article answer the following questions:
1) The authors designed the study to have a “power of more than 80%“. What does this mean?
2) What was the planned type 1 error rate in this study?
3) What is a type 2 error and how is it related to power?
4) What are the determinants of sample size in this study? How does varying the estimates of these components affect sample size?
5) The authors use a variety of statistical tests (chi-square, Fisher’s exact, t-tests, etc) to analyze the data. In general, what do statistical tests do?

Review Table 2 and answer the following questions:1) The primary outcome occurred in 1.92/100 person-yrs in the control group compared to 1.83/100 person-yrs in the intervention group. The p-value associated with this comparison is 0.51. What does this p-value mean? Can p-values be used to detect bias in the study?
2) The hazard ratio comparing the intervention group to the control group for the primary outcome is 0.95 with a 95% confidence interval of 0.83-1.09. What does this confidence interval tell you about the effect? Can confidence intervals be used to detect bias in the study?

Extra Credit:
List the 4 things that can explain study findings