Econ 703
Final Study Guide
Professor: Cathy Xue
1
Introduction
1.1
Population vs. Sample
•
A
population
is simply a set of people, places, companies, things etc. that we are interested in.
•
A
sample
is a subset of a population. You get data from this subset (or portion) of the population
to form a dataset and do analysis.
•
a
census
is a data set that covers an entire population, not just some of the observations.
1.2
Descriptive Statistics vs. Statistical Inference
•
If we have a sample, or a census, and only want to describe the observations in that specific data
set, then the statistics we estimate are called
descriptive statistics
.
•
If we have a sample and want to say something about the population. This is called
inferential
statistics
or
statistical inference
or
inference
.
1.3
Three Levels of Data (Quantitatively)
•
Nominal Level Data
- Can be used for classification purposes only.
•
Ordinal Level Data
- Can be used for classification and also ranking/ordering.
•
Interval Level Data
- This data allows us to classify, and assign rank/order, quantify distances,
and perform various kinds of calculations. Interval data is always numerical.
•
Nominal level and ordinal level data are called
qualitative data
since we can’t do much math with
them. Interval level data is called
quantitative data
. Mathematically, we can do most operations
with them.
1.4
Three Types of Data (Structurally)
•
Cross-Sectional
: The data is collected at the same time and you only observe each unit once.
•
Time Series
: You observe only one unit, but you observe it at many different points in time.
•
Panel Data
: You observe multiple units, and you observe these units at multiple points in time.
1

Econ 703 Statistics Foundations
Professor: Cathy Xue
2
Tables and Graphs
2.1
Tables
•
Class Interval
•
Midpoint
•
Frequency
•
Relative Frequency
•
Cumulative Frequency
2.2
Graphs for Quantitative Data
•
Histogram
•
Stem and Leaf Plot
•
Scatter Plot
2.3
Graphs for Qualitative Data
•
Pie Chart
•
Bar Chart
3
Descriptive Statistics
3.1
Center of a Distribution
•
Mean
- The average.
μ
denotes the population mean, ¯
x
denotes the sample mean.
¯
x
=
1
n
n
i
=1
x
i
=
1
n
(
x
1
+
x
2
+
· · ·
+
x
n
)
•
Median
- The middle observation when the observations are in ascending order. If there are even
numbers of observations, median is the average of the two numbers that are in the middle.