Chapter 7 Descriptive Statistics

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Chapter 7 Descriptive Statistics

• Epidemiology Provides a basis for theory and
  methodology. Informed decision making. Closely
  tied to clinical methods.
• Biostatistics Provides a way to test and
  correlate the data collected and conclusions
  reached.
• Computers and their use Construct and use
  databases, get reports, statistical programs.

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Empirical Research

• Uses prospective studies
• There is an experimental research design
• Uses statistical methods to test data

3
Statistics

• Inferential statistics Uses mathematical
  formulas applied to parametric data. Makes a
  statement about levels of probability. Often
  predictive in nature.
• Descriptive statistics Used to develop rates,
  ratios, percentages. Data from chapters 4 5.
  Describes the frequency and distribution of data.

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Variables used in descriptive statistics

• Age
• Gender
• Season
• Income
• Race
• Occupation
• Dates

• Education
• Religion
• Family issues
• Marital status
• Geography

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Data Types Nominal

• Classify data that lacks order and cant be
  numerically arranged
• Categorical data, not for calculations
• Survey questions classifying people
• Race, religion, occupation type, etc

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Ordinal Scales

• Provides order to the data
• Numbers are assigned to categories
• Often a Likert scale is used
• Health surveys, Apgar scores, severity of a
  headache
• Quality of service

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Interval scales

• Divides data into equal distances between
  categories
• IQ measurements
• Amount someone smokes in a group of smokers
• The value between points may not be linear

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Ratio scales

• Goes from zero to
• There is an equal distance between points
• Exam scores, weight, temperature, blood pressure,
  elapsed time
• Important for most descriptive statistics

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Parametric Vs. Nonparametric

• Used with interval and ratio scales
• Random sampling
• Normal distribution
• Variance between groups is known

• Used with nominal and ordinal scales
• Tells you proportions around the mean
• Data is drawn from a group at random

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Central Tendency

• Mean Sum of all the n divided by n. Sensitive to
  extreme values. Used with interval and ratio
  scales.
• Mode Number of scores that occur most often.
  Used with all four scales
• Median Divides the list in half.The number in
  the middle is used. Used with ordinal, interval
  and ratio scales

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Measures of Dispersion

• Range Highest-lowest scores
• Deviation from the mean how far a score is
  located from the mean
• Sum of squares How far the normal distribution
  is spread out. Its the sum of the squared
  deviations from the mean.
• Variance The average of the squared deviations.
• Standard deviation Square root of the variance.

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Central Tendency

• Percentile ranking provides a reference point,
  above or below
• Z score Tells you relative standing. The number
  of standard deviations below or above the mean.
• Skewness figures 7.2, 7.3, 7.4, and 7.5

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Statistical Applications

• Microsoft Excel
• SPSS (Statistical Program for the Social
  Sciences)
• SAS (Statistical Application for Science)

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Charts and Graphs

• A picture says a thousand words
• A color chart says 10,000 words to a busy doctor
  or executive
• Pie charts
• Line graphs
• Bar charts
• 3-D stuff