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Chapter 10 Descriptive Statistics

Chapter 10 Descriptive Statistics. Numbers One tool for collecting data about communication phenomena Capture quality, intensity, value, or degree Only meaningful if they are interpreted Operationalizations specify how data are collected and become numerical. Looking at a Dataset.

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Chapter 10 Descriptive Statistics

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  1. Chapter 10Descriptive Statistics • Numbers • One tool for collecting data about communication phenomena • Capture quality, intensity, value, or degree • Only meaningful if they are interpreted • Operationalizations specify how data are collected and become numerical

  2. Looking at a Dataset

  3. Normal Curve • Also known as bell curve • A theoretical distribution of scores • Majority of cases distributed around the peak in the middle • Progressively fewer cases moving away form the middle • Symmetrical – one side mirrors the other • Mean, median, and mode have the same value

  4. Normal Curve

  5. Skewed Distributions • Curve is asymmetrical • Positively skewed curve – very few high scores • Negatively skewed curve – very few low scores

  6. Descriptive Statistics • Summary information for each variable • Number of cases • Central tendency • Dispersion • Used by researcher to describe variables • Used in statistical tests to analyze differences and relationships between variables

  7. Number of Cases • Number of cases for which data are reported • Represented by n or N • n = 231 • Cases may be people, speaking turns, episodes – any phenomenon studied

  8. Measures of Central Tendency • Mean • Arithmetic mean or average • Most sensitive to extreme scores • Median • Middle of all scores on one variable • Mode • Score or scores that appear most often

  9. Measures of Dispersion • Describes the variability or spread of scores • Should be reported with mean • Range • Highest to lowest score • Standard deviation or sd • If sd = 0, all scores are the same • Larger the sd, the more the scores differ from the mean

  10. Standard Deviation

  11. Standard Deviations • Theoretical normal curve is divided into equal standards • The more normal a distribution of scores, the more this theoretical property applies • 68.26% of scores fall within +1 to –1 standards

  12. Application of Descriptive Statistics • Reported in methods section of research report • Mean, sd, range, and n should be reported for each variable • Frequencies – the number of times a particular value of a variable occurs • Percentages – often used to describe characteristics or attributes of participants

  13. Crunching Numbers • Need calculator with square root key, spreadsheet program, or statistics program • Researcher must select appropriate descriptive statistic and test • Researcher must indicate which data are to be calculated or tested • Wrong input = error in results

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