1

PAUF 610 TA

1st Discussion

2

3

Population & Sample

• Population includes all members of a specified group. (total collection of objects/people studied)– E.g. MSPP students

• Sample represents only a subset of the population of interest. (some fraction of the population)– E.g. PUAF 610 students

4

Type of Statistics

• Descriptive statistics summarize numerical information.

• Inferential statistics allows to draw inferences about a population based on a sample of that population.

5

Three main types of data

• Cross-sectional data

• Time-series data

• Panel data

6

Cross-sectional data• represent measurements taken at one

time across multiple subjects.• E.g. GDP for US, China, UK, Russia in

2009

7

Time-series data• include measurements for the same

subject over a period of time.• E.g. GDP for US from 2000 to 2009.

8

Panel data• combine two previous types and provide

measurements for multiple subjects over time.

• E.g. GDP for US, China, UK, Russia from 2000 to 2009.

9

Constant & Variable

• If a property (or characteristic) of a object stays the same it is called a constant.– E.g. hours per day

• If it takes on different values it is called a variable. (A variable can take on different values for different individuals)– E.g. temperature, gender

10

Types of Variables

• Quantitative (Numerical)

• Qualitative (Categorical)

11

Quantitative

• Numeric value that makes sense to do arithmetic operations (+, -, x, /) – E.g. height, weight, age, income

12

Qualitative

• Records which of several groups or categories to which an individual belongs– E.g. gender, race, hair color, field of study

13

Measurement scales

13

Qualitative data (unordered or ordered discrete categories)

•Nominal - numbers are used as labels for the elements in the data system; measured only in terms of whether the individual items belong to certain distinct categories (e.g. gender)

•Ordinal – can be ordered on the amount of the property being measured and values are assigned in this same order.(e.g. ratings)

14

Measurement scales

14

Quantitative data (variables have underlying continuity)

•Interval - numbers indicate rank order, and distances between them have meaning with respect to the property being measured (temperature)

•Ratio – numbers have all three properties of the real-number system (order, equal distances between units and fixed origin)

15

intervalcontinuous

numerical proportiondiscrete

datadichotomous

nominalnon-dichotomous

categoricalordinal

16