Download Descriptive Statistics: Graphical Techniques for Quantitative Data and more Exams Statistics in PDF only on Docsity! 1. Data, Graphical Descriptive Techniques Introduction Descriptive statistics involves the arrangement, summary, and presentation of data to enable meaningful interpretation and to support decision making. Descriptive statistics methods make use of graphical techniques numerical descriptive measures The methods presented apply to both the entire population the population sample Types of data A variable is a characteristic of population or sample that is of interest for us, for instance, Cereal choice Capital expenditure The waiting time for medical services Data - the actual values of variables Quantitative data are numerical observations Qualitative data are categorical observations Quantitative data Age - income 55 75000 42 68000 . . . . Weight gain +10 +5 . . 1 Qualitative data Person Married/unmarried 1 yes 2 no 3 no . . . . Professor Rank 1 Lecturer 2 Full 3 Assistant . . . . With qualitative data, all we can do is to calculate the proportion of data that falls into each category. Lecturers Assistant Associate Full Total 15 25 5 15 60 25% 41.67 8.33% 25% 100% Knowing the type of data is necessary to properly select the technique to be used. Type of analysis allowed for each type of data Quantitative data - arithmetic calculations Qualitative data - counting the number of observation in each category Cross-sectional and Time-Series Data Cross-sectional data is collected at a certain point in time, for example, Marketing survey (observe preferences by gender, age) Test score in a statistics course Starting salaries of an MBA program graduates Time series data is collected over successive points in time, for instance, Weekly closing price of gold Amount of crude oil imported monthly 2 20 7
Frequency
3
|
C1
Skewness
© Positively skewed <—
Frequency
&
|
© Negatively skewed >
Number of modal classes (A modal class is the one with the largest number of observations) unimodal histogram bimodal histogram 6 Bell shaped histogram Many statistical techniques require that the population be bell shaped. Drawing the histogram helps verify the shape of the population in question 7
