Bài giảng Chapter 10 Descriptive Statistics

Chapter 10Descriptive StatisticsNumbers One tool for collecting data about communication phenomenaCapture quality, intensity, value, or degreeOnly meaningful if they are interpretedOperationalizations specify how data are collected and become numerical1Looking at a Dataset2Normal CurveAlso known as bell curveA theoretical distribution of scoresMajority of cases distributed around the peak in the middle Progressively fewer cases moving away form the middleSymmetrical – one side mirrors the otherMean, median, and mode have the same value3Normal Curve4Skewed DistributionsCurve is asymmetricalPositively skewed curve – very few high scoresNegatively skewed curve – very few low scores5Descriptive StatisticsSummary information for each variableNumber of casesCentral tendencyDispersionUsed by researcher to describe variables Used in statistical tests to analyze differences and relationships between variables6Number of CasesNumber of cases for which data are reportedRepresented by n or Nn = 231Cases may be people, speaking turns, episodes – any phenomenon studied7Measures of Central TendencyMeanArithmetic mean or averageMost sensitive to extreme scoresMedianMiddle of all scores on one variableModeScore or scores that appear most often8Measures of DispersionDescribes the variability or spread of scoresShould be reported with meanRangeHighest to lowest scoreStandard deviation or sdIf sd = 0, all scores are the sameLarger the sd, the more the scores differ from the mean9Standard Deviation10Standard DeviationsTheoretical normal curve is divided into equal standardsThe more normal a distribution of scores, the more this theoretical property applies68.26% of scores fall within +1 to –1 standards11Application of Descriptive StatisticsReported in methods section of research reportMean, sd, range, and n should be reported for each variableFrequencies – the number of times a particular value of a variable occursPercentages – often used to describe characteristics or attributes of participants12Crunching NumbersNeed calculator with square root key, spreadsheet program, or statistics programResearcher must select appropriate descriptive statistic and testResearcher must indicate which data are to be calculated or testedWrong input = error in results13