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What is a Confidence Interval?

On Monday we talked about how p-values tell us the probability of obtaining the result if the null hypothesis (the status quo) is true.  Today we turn our attention to the confidence interval and the additional information using a confidence interval provides. There are two things you need to remember to make sense of a [...]

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What is a p-value?

We’ve talked about data and the descriptive statistics.  We’ve talked about the measures we use and stratifying by populations and sub populations to assess disparities.  We talked about the types of studies and last week we moved into our first statistical test of a hypothesis, the chi-square.  Today we will talk about how we know [...]

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A Literature Example

In this study, Pregnancy outcome in women with previous one cesarean section, the authors did many statistical comparisons of the data. One comparison is easily understood with a chi-square – does having a previous vaginal delivery increase the success rate of VBAC?

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Odds And Risk Ratios

Before we move into our example study we need to spend a few minutes on the difference between risk and odds.  It can be difficult to understand, but it is important for interpretation of studies. When research presents risk, what is being presented is the number of people with the selected characteristic divided by the [...]

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The Chi-Square Statistic

  We have been talking about statistics, and how to understand the statistics piece of a research article. Today we will start looking at the most common statistical tests used in health-care research. We will not talk about how to do these tests. Instead we will focus on how and why these tests are used. [...]

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Why we use statistics

You’ve designed your study, recruited a sample and collected data. Maybe your study finds 20% of the women who gave birth at a birth center had at least a second degree tear, while 25% of the women who gave birth at a hospital had at least a second degree tear.  The next question you need [...]

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Types of Studies

No doubt you’ve seen something like this hierarchy of studies from Duke University’s Introduction to Evidence-Based Practice site. In this hierarchy, the studies are classified by the type of sample used. Types of Samples In a case study or case report, the sample is one or two individuals who experienced something unusual or noteworthy. In a [...]

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Disparities

When we compare two populations and find a difference in a health outcome, we want to look more closely to determine if that outcome difference is due to a difference in health related characteristics or non-health related characteristics.  When the difference is due to something other than health characteristics, the difference is considered a disparity. [...]

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Populations and Risk

Last time we talked about the difference between incidence and prevalence.  Today, we will look at how we can use these descriptive measures to understand differences in risk. Remember from Monday that the population is the group of individuals you would like to learn about. As midwives, we are often interested in specific groups of [...]

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Understanding Data – the measure

We need to talk about what might be considered the “back end” of statistics. That is, how did the data come to be? Types of Observations Data is simply a collection of variables, grouped by observation.  In health care, the observation is usually a “case” or a “person”. Researchers make each observation in a variety [...]

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