Statistical Significance – How important is the p-value and what does it mean?
A large group of scientists now agree that statistical significance is confusing research conclusions from all sorts of studies, including those on vitamin D!
A statement released by the American Statistical Association in 2016 warned against the misuse of statistical significance and P values. Since then, a commentary article published in Nature called for the abandonment of the concept of statistical significance. Prior to publication, the article was signed and endorsed by more than 850 statisticians, researchers, and other scientists from around the world – whose past or present work depends on statistical modelling.
The article highlights the problem in detail, and states that scientists
“should never conclude there is ‘no difference’ or ‘no association’ just because a P value is larger than a threshold such as 0.05 or, equivalently, because a confidence interval includes zero. Neither should we conclude that two studies conflict because one had a statistically significant result and the other did not. These errors waste research efforts and misinform policy decisions.”
Source: V. Amrhein et al.
What is “statistical significance” and what does it mean for vitamin D?
“Significance” in scientific research terms is a computation done during data analysis to evaluate the strength of the evidence. It is also called the P value.
An example of how a P value can be reported can be seen in the following statement, taken from the abstract of Lappe et al., JAMA 2017, a study looking at cancer incidence among 2303 women over a 4 year period, using either vitamin D + calcium or placebo:
“A new diagnosis of cancer was confirmed in 109 participants, 45 (3.89%) in the vitamin D + calcium group and 64 (5.58%) in the placebo group (difference, 1.69% [95% CI, -0.06% to 3.46%]; P=.06).”
The P value is a probability, a percentage. In this calculation, the P value was .06, which means that there is a 6% chance that this result (30% reduction in cancer in the vitamin D + calcium group) was due to chance – not the actual treatment. In a different wording, that means you are 94% sure it was NOT chance! It is standard practice within the scientific community that P=.05 or less is an accepted amount for study results to have “significance” and anything higher than P=.05 is “not statistically significant.” There is no middle ground, it is black or white.
Does “not statistically significant” mean “no difference”?
The abstract, or summary of the paper, is often all that people see unless they subscribe to the journal or pay for the paper. When a layman reads this text, it can be understood to mean that there wasn’t a meaningful reduction in risk. For example, the conclusion from the Lappe et al. abstract reads:
“Conclusions and Relevance – Among healthy postmenopausal older women with a mean baseline serum 25-hydroxyvitamin D level of 32.8 ng/ml, supplementation with vitamin D3 and calcium compared with placebo did not result in a significantly lower risk of all-type cancer at 4 years. Further research is necessary to assess the possible role of vitamin D in cancer prevention.”
A look at the chart below illustrating the results from this study may portray a different conclusion.
The initial analysis by treatment group showed a 30% reduction, with a P value of .06. Because the P value was greater than the .05 cut-off, it was labeled “not statistically significant.”
However, when participants who withdrew from the study or developed cancer within the first 12 months were excluded from analysis, the study reports a 35% reduction in cancer in the vitamin D + calcium group compared to the placebo group (P-value = .047). This was a “statistically significant” difference.
Why would they take out year 1 data?
The chart above explains it well if you are a visual person. For the two groups, cancer incidence was almost identical in the first year. You can see the yellow and blue lines are on top of each other. After a year they start to separate. Simply put, removing the first year excludes those whose cancer was already progressing but not yet diagnosed, and it allowed time for vitamin D to “do its job.”
Even without removing the first year of data, we ask you this… should the original conclusion showing a 30% reduction in cancer be ignored because the P value was .01 greater than what scientists have labeled as acceptable? How would you interpret this information to help you make your own health decisions?
How does this apply to D*action?
One of the ways to improve statistical power (i.e. the ability to detect a significant result if one exists) is to use a larger sample size. The more people that test their levels and fill out the D*action questionnaire, the better research we are able to conduct!
Could Vitamin D Make a Difference for YOUR Health?
Correcting a vitamin D deficiency at any age and any time of life may decrease potential disease incidence and severity, and improve outcomes! Test your vitamin D level today, learn what steps to take to improve your level, and take action to achieve and maintain a vitamin D level of 40-60 ng/ml (100-150 nmol/L).
Using the GrassrootsHealth Custom Kit Builder, you can create a test kit that measures your status of vitamin D and other important nutrients (such as omega-3s, zinc and magnesium), as well as your CRP level to measure inflammation. Click here to build and order your test kit today – measure your status and take the steps necessary to improve them if needed; make an impact on your health today and for your future! When you know what your levels are, you can determine next steps to take and how much supplementation may be needed if you are not at your target levels.
Enroll now with the Full Immune Boost Panel (which includes tests for vitamin D, Omega-3 Index, magnesium, zinc, selenium, copper, and hsCRP), and get 10% off when you use coupon code BoostTen at checkout.
What Does it Take YOU to Get Your D to 40 ng/ml (100 nmol/L)?Did you know your health could be greatly affected by making sure you have a vitamin D level of at least 40 ng/ml (100 nmol/L)? Help us help you.
STEP 1 - Do you know what your vitamin D level is? If not, be sure to test today to find out.
STEP 2 – Determine your target level. Are you at your target level? Experts recommend a level of at least 40-60 ng/ml (100-150 nmol/L).
STEP 3 – Need to boost your level? Use the D*calculator to see how much vitamin D it may take to reach your target. Opt for the Loading Dose for a quicker boost.
STEP 4 – Optimize how your body absorbs and utilizes vitamin D with co-nutrients and these simple steps.
STEP 5 – Re-Test! This is an important step to make sure you have reached your target level, and to ensure you are not taking too much! Re-testing after 3-4 months is recommended.
STEP 6 – Adjust, Repeat…
Give your immune system the nutrients it needs to support a healthy you and protect yourself from unnecessary diseases, especially COVID-19.
The first Randomized Controlled Trial on vitamin D and COVID-19 has shown a 96% lower risk of ICU admission for those receiving vitamin D (as 25(OH)D to quickly boost vitamin D blood levels) along with the standard treatment, compared to those receiving standard treatment alone.
These results support many previous observational studies showing a relationship between vitamin D levels and intake and COVID-19 severity.
GrassrootsHealth Nutrient Research Institute has launched the new Immune Boost project with the use of our myData-myAnswers nutrient health system that nearly 15,000 people are already using for their health. Specific markers that influence immune health are suggested for testing as part of this project including:
- Vitamin D
- Omega-3 Index
- Essential elements magnesium, selenium, and zinc
Our goal is to demonstrate how one can use the Nutrient Research Model established by Dr. Robert Heaney to show the effect of vitamin D serum levels of at least 40 ng/ml (100 nmol/L) on risk reduction for all ethnicities in the population. Status and intake of other nutrients will also be analyzed for any type of relationship to immune status and symptom severity. Join the project today!
Please let us know if you're interested in helping sponsor this project.
Through GrassrootsHealth Nutrient Research Institute, you can also test your essential elements magnesium, copper, zinc and selenium, toxins such as lead, mercury and cadmium, as well as your omega-3 levels, inflammation levels and thyroid stimulating hormone (TSH) level. Find out your levels today! Log on to the test selection page (click the link below) to get your tests and see for yourself if your levels can be improved.
Make sure you track your results before and after, about every 6 months!
How can I track my nutrient intake and levels over time?
To help you track your supplement use and nutrient levels, GrassrootsHealth has created the Personal Health Nutrient Decision System called
For each specific supplement, you can track what days you take it, how much, and many other details. This will help you know your true supplemental intake and what patterns of use work for you to reach and maintain optimum nutrient levels. Check it out today!