Ch1 Introduction to Statistics
1.1 Populations and Samples
l population:
.
(the population is often too large for us to examine each of its members)
l sample:
.
(In order for the sample to be informative about the total population, it must be, in
some sense, representative of that population)
1.2 Frequency Tables and Graphs
eg. The following data represent the number of days of sick leave taken by each of
50 workers of a given company over the last 6 weeks:
2, 2, 0, 0, 5, 8, 3, 4, 1, 0, 0, 7, 1, 7, 1, 5, 4, 0, 4, 0, 1, 8, 9, 7, 0,
1, 7, 2, 5, 5, 4, 3, 3, 0, 0, 2, 5, 1, 3, 0, 1, 0, 2, 4, 5, 0, 5, 7, 5, 1
l
raw data
l
frequency table:
.
frequency column represents
.
eg. A Frequency Table of Sick Leave Data
Value
0
1
2
3
4
Frequency
12
8
5
4
5
Value
5
6
7
8
9
Note. the sum of all the frequencies is 50,
1
Frequency
8
0
5
2
1
.
Ch1 Introduction to Statistics
l
line graph: a graph which plots the
horizontal axis and indicates the
vertical line.
on the
by the height of a
l
bar graph: frequencies are represented by
l
frequency polygon: graph which plots the frequencies of the different data
values and then connects the plotted points with straight lines.
2
Ch1 Introduction to Statistics
l
relative frequency graph: relative frequency    is plotted versus  , where 
represents
and
 represents
eg. relative frequency polygon
l
pie chart:
If a data value has relative frequency f/n, then its sector can be obtained by
setting the angle at which the lines of the sector meet equal to
degrees.
Exercise1 This frequency distribution shows the number of pounds of each snack
food eaten during the Super Bowl. Construct a pie graph for the data.
Snack
Potato chips
Tortilla chips
Pretzels
Popcorn
Snack nuts
Pounds (frequency)
11.2
8.2
4.3
3.8
2.5
Total n = 30.0
million
million
million
million
million
million
:
3