# Effect Size and Practical and Statistical Significance

Discussion 1 – Week 2

COLLAPSE

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Effect Size and Practical and Statistical Significance

Effect size refers to the strength of a relationship between two variables. It can be expressed through a difference or ratio. Odds ratios, which compare the likelihood of the same event occurring within two separate groups, reflect effect size.

Consider the following two scenarios:

1. Ten thousand people participated in a survey in which they were asked whether they use a vitamin C supplement and also whether they had experienced cold symptoms the previous winter. The study demonstrated an odds ratio of 1.08 and a p-value of 0.04. Based on this, the researchers recommended the use of vitamin C supplements to avoid experiencing a cold next winter.
2. Fifty people participated in a survey about stress and a diagnosis of high blood pressure. This study resulted in an odds ratio of 1.6 and a p-value of 0.07. Based on these results, the study was not published and the researchers moved on to other work.

These two hypothetical situations are extremes, but they illustrate the difference between practical and statistical significance. Practical significance is inferred from the size of the effect, while statistical significance is inferred from the precision of the estimate. The effect size reflected in the odds ratio in the first case was 0.08, or an 8% difference in likelihood of a cold based on vitamin C supplementation (small practical difference of 8%, but statistically significant, with a p-value of 0.04). The effect size in the second case was 0.6, or a 60% difference in the likelihood of a diagnosis of high blood pressure based on stress (large practical difference of 60%, but small statistical significance, with a p-value of 0.07).

For this Discussion, review this week’s Learning Resources. Consider effect size and how to determine whether practical or statistical significance exists. Select a public health research study from one of the peer-reviewed journal articles listed in the Week 2 Resources. Consider whether effect size is practically or statistically significant in the study.

By Day 4

Post a brief summary of the article you selected. Then briefly explain the interrelationship between the effect size, power, and sample size in the article. Explain whether the effect size was practically significant, statistically significant, or both, and why. Using the article you selected as an example, support the importance of incorporating both practical and statistical significance in study conclusions.

Be sure to support your postings and responses with specific references to the Learning Resources.

By Day 6

Respond to your colleagues in one or more of the following ways:

• Expand on the colleague’s posting with additional insight and resources.
• Offer polite disagreement or critique, supported with evidence.

In addition, you may also respond as follows:

• Offer and support an opinion.
• Validate an idea with your own experience.
• Make a suggestion or comment that guides or facilitates the discussion.

Review and reflect on your colleagues’ responses to your initial posting. Note what you have learned and/or any insights you have gained as a result of the comments made by your colleagues. (No posting is required for this reflection.)

Click on the Reply button below to reveal the textbox for entering your message. Then click on the Submit button to post your message.

Discussion 2 – Week 2

COLLAPSE

To enhance your learning experience, the Study Group Area provides a forum where you can ask questions related to the weekly content. Participating in the Study Group Area may help you complete your assignments and master the weekly learning objectives.

Within each week, be sure to review all your learning resources to help you fully understand the topic.

By Day 5

Share with your colleagues any questions, challenges, insights, or advice related to the week’s topic