S519: Evaluation of Information Systems

Social Statistics

Ch4: Chart

Chart

Label everything One graph communicate one idea Keep things balanced Simple is best

A picture is worth a thousand words

Frequency distribution

Frequency distribution is a method to represent the frequency of certain scores.

When you have a data set, such as a testing scores,

Class intervals Number of intervals: 5, 10, 20 Value of interval=range/number of intervals

Exercise

50 scores Set class intervals Create a histogram using your hand Using Excel to do that

Score47244417635383536101114143030323334323131151617

16151918162525262627292928292720212121242423202120

A histogram

Excel for Histogram

First, define your bins The starting point of a bin Data analysis Toolpak histogram

Skewness

Skewness (S-p98-Fig 4.15) Measure of the lack of symmetry of a distribution mean>median>mode positively skewed mean<median<mode negatively skewed

Kurtosis

Kurtosis (S-p99-Fig 4.16) flat or peaked of a distribution

Variability

Variability (S-p97-Fig 4.14)

Frequency distribution

Excel: SKEW() and KURT() As a general rule, we will conclude that the

distribution is significantly skewed or kurtotic if the statistic is greater than three times its standard error.

For example, your rule to determine if the distribution is actually skewed (to confirm your visual impression) is:  IF skew > ± 3 * SE_Skewness THEN it is skewed.

SPSS can do this