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Basic Data Analysis: Descriptive Statistics Types of Statistical Analysis Descriptive Inferential: Test of Differences Test of Associative Predictive Pre Descriptive Statistics Data entry - Data coding (data code book). Data matrix Descriptive statistics - “describe” the data, portray an average respondent (data reduction): Summarizes Conceptualizes Communication Interpolation/extrapolation Descriptive Statistics Statistical concepts: Measures of Central Tendency Measures of Variability Other Descriptive Measures Measures of Central Tendency Applies to any measure that reflects a typical or frequent response Mode: the number that appears most often Median: the value whose occurrence lie in the middle of a set of numbers (half above and half below) Mean: arithmetic average of a set of numbers Measures of Central Tendency Mean: arithmetic average of a set of numbers X=sample mean m = Population mean Measures of Variability Reveal the typical differences between values in a data set Frequency Distribution: tabulation of the number of times that each different value appears in a data set, shown as a percentage Range: difference between the lowest and highest value in a data set Measures of Variability Standard Deviation: indicates the degree of variation or diversity in the values in such as way as to be translatable into a normal curve distribution With a normal curve, the midpoint (apex) of the curve is also the mean and exactly 50% of the distribution lies on either side of the mean. Normal, bellshaped curve 50% 50% Midpoint (mean) Normal Curve and Standard Deviation Number of standard deviations from the mean Percent of area under the curve Percent of area to the right or left +/- 1.00 st dev 68% 16% +/- 1.64 st dev 90% 5% +/- 1.96 st dev 95% 2.5% +/- 2.58 st dev 99% 0.5% Other Descriptive Measures Measures of skewness Is the curve really bell-shaped or does it “skew” to one side or the other? The closer the number given for skewness is to zero, the closer the distribution is to being bell-shaped. A positive skewness means that the distribution has a tail to the right while a negative skewness means it has a tail to the left Other Descriptive Measures Kurtosis indicates how pointed or peaked the distribution. A kurtosis value of zero or close to zero indicates that the distribution is bell-shaped. When to use what Type of Measurement Nominal Ordinal Interval/Ratio Central Tendency Mode Median Mean Variability Frequency or percentage distribution Percentage distribution Standard deviation Microsoft Excel Menu: Tools, Data Analysis, Descriptive Statistics If Data Analysis is not present under Tools Bar then go to Tools, Add-ins check Analysis Toolpak and Analysis Toolpak VBA click OK Data analysis should appear under Tools now