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KEY CONCEPTS

KEY CONCEPTS

  • Image not available.All observations of subjects in a study are evaluated on a scale of measurement that determines how the observations should be summarized, displayed, and analyzed.

  • Image not available.Nominal scales are used to categorize discrete characteristics.

  • Image not available.Ordinal scales categorize characteristics that have an inherent order.

  • Image not available.Numerical scales measure the amount or quantity of something.

  • Image not available.Means measure the middle of the distribution of a numerical characteristic.

  • Image not available.Medians measure the middle of the distribution of an ordinal characteristic or a numerical characteristic that is skewed.

  • Image not available.The standard deviation is a measure of the spread of observations around the mean and is used in many statistical procedures.

  • Image not available.The coefficient of variation is a measure of relative spread that permits the comparison of observations measured on different scales.

  • Image not available.Percentiles are useful to compare an individual observation with a norm.

  • Image not available.Stem-and-leaf plots are a combination of frequency tables and histograms that are useful in exploring the distribution of a set of observations.

  • Image not available.Frequency tables show the number of observations having a specific characteristic.

  • Image not available.Histograms, box plots, and frequency polygons display distributions of numerical observations.

  • Image not available.Proportions and percentages are used to summarize nominal and ordinal data.

  • Image not available.Rates describe the number of events that occur in a given period.

  • Image not available.Prevalence and incidence are two important measures of morbidity.

  • Image not available.Rates must be adjusted when populations being compared differ in an important confounding factor.

  • Image not available.The relationship between two numerical characteristics is described by the correlation.

  • Image not available.The relationship between two nominal characteristics is described by the risk ratio, odds ratio, and event rates.

  • Image not available.Number needed to treat is a useful indication of the effectiveness of a given therapy or procedure.

  • Image not available.Scatterplots illustrate the relationship between two numerical characteristics.

  • Image not available.Poorly designed graphs and tables mislead in the information they provide.

PRESENTING PROBLEMS

Presenting Problem 1

Life expectancy varies across regions of the United States. Davids et al (2014) examined the Community Health Status Indicators (CHSI) to Combat Obesity, Heart Disease, and Cancer to determine opportunities to improve health status and life expectancy based on known social determinants of health. They found a link between life expectancy and poverty, educational level, and the racial composition of the county.

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Presenting Problem 2

Many patients with chronic diseases do not engage in self-management activities. Bos-Touwen and associates (2015) investigated the characteristics of patients that participate in self-management programs for a number of chronic diseases including: type-2 Diabetes Mellitus (DM-II), Chronic Obstructive Pulmonary Disease (COPD), Chronic Heart Failure (CHF), and Chronic Renal Disease (CRD). They used a survey tool called the 13-item Patient Activation Measure (PAM-13) as well as demographic, clinical, and psychosocial variables.

The data for ...

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