vdoc

03.05.2023 Views

204 Part IV: Quality AssuranceFinally, note that the data in the above example contains two values, 250 and300 thousand dollars, that seem to be the sales of top-performing sales personnel.These two large values may be considered as extreme values.In this case, the mean of these data is given byX – = (7 + 8 + 10 + 12 + 12 + 15 + 15 + 16 + 17 + 18 +19 + 20 + 22 + 25 + 250 + 300)/16 = 47.875Since the mean of 47.875 is so much larger than the median of 16.5 it is obvious thatthe mean of the data has been adversely affected by the extreme values. Since inthis case the mean does not adequately represent the measure of centrality of thedata set, the median would more accurately identify where the center of the datais located.Furthermore, if we replace the extreme values of 250 and 300, for example,with 25 and 30 respectively, then the median does not change whereas the meanbecomes $16,937. Thus, the new data obtained by replacing 250 and 300 with 25and 30 respectively did not contain any extreme values. Therefore, the new meanvalue is more consistent with the true average sales.Mode. The mode of a data set is the value that occurs most frequently. Mode isthe least used measure of centrality. When products are produced via massproduction, for example, clothes of certain sizes, rods of certain lengths, and soon, the modal value is of great interest. Note that in any data set there may be nomode, or conversely, there may be multiple modes. We denote the mode of a dataset by M 0 .Part IV.A.1EXAMPLE 18.5Elizabeth took five courses in a given semester with 5, 4, 3, 3, and 2 credit hours. Thegrade points she earned in these courses at the end of the semester were 3.7, 4.0, 3.3,3.7, and 4.0 respectively. Find her GPA for the semester.Solution:Note that in this example the data points 3.7, 4.0, 3.3, 3.7, and 4.0 have different weightsattached to them, that is, credit hours for each course. Thus, to find Elizabeth’s GPAwe can not simply find the arithmetic mean. Rather, in this case we shall find the meancalled the weighted mean, which is defined as:XwwX1 1+ wX2 2+ … + wXn=w + w + … w1 2nnwXi i=wi(18.3)where w 1 , w 2 , …, w n are the weights attached to X 1 , X 2 , . . . , X n respectively. In thisexample, the GPA is given by:( )+ ( )+ ( )+ ( )+ ( )537 . 440 . 333 . 337 . 240 .X w=5+ 4+ 3+3+2= 3. 735.

Chapter 18: A. Basic Statistics and Applications 205Find the mode for the following data set:EXAMPLE 18.63, 8, 5, 6, 10, 17, 19, 20, 3, 2, 11Solution:In the given data set each value occurs once except 3 which occurs twice.Thus, the mode for this set is:M 0 = 3Find the mode for the following data set:EXAMPLE 18.71, 7, 19, 23, 11, 12, 1, 12, 19, 7, 11, 23Solution:Note that in this data set, each value occurs the same number of times. Thus, in this dataset there is no mode.EXAMPLE 18.8Find modes for the following data set:5, 7, 12, 13, 14, 21, 7, 21, 23, 26, 5Solution:In this data set 5, 7, and 21 occur twice and the rest of the values occur only once.Thus, in this example there are three modes, that is,Part IV.A.1M 0 = 5, 7, and 21Note that there is no mathematical relationship as such between the mean,mode, and median. However, the values of mean, mode, and median do provideus important information about the potential type or shape of the frequency distributionof the data. Although the shape of the frequency distribution of a dataset could be of any type, most frequently we see the three types of frequency distributionsshown in Figure 18.1.The location of the measures of centrality as shown in Figure 18.1 providethe information about the type of data. A data set is symmetric when the valuesin the data set that lie equidistant from the mean, on either side, occur with equal

Chapter 18: A. Basic Statistics and Applications 205

Find the mode for the following data set:

EXAMPLE 18.6

3, 8, 5, 6, 10, 17, 19, 20, 3, 2, 11

Solution:

In the given data set each value occurs once except 3 which occurs twice.

Thus, the mode for this set is:

M 0 = 3

Find the mode for the following data set:

EXAMPLE 18.7

1, 7, 19, 23, 11, 12, 1, 12, 19, 7, 11, 23

Solution:

Note that in this data set, each value occurs the same number of times. Thus, in this data

set there is no mode.

EXAMPLE 18.8

Find modes for the following data set:

5, 7, 12, 13, 14, 21, 7, 21, 23, 26, 5

Solution:

In this data set 5, 7, and 21 occur twice and the rest of the values occur only once.

Thus, in this example there are three modes, that is,

Part IV.A.1

M 0 = 5, 7, and 21

Note that there is no mathematical relationship as such between the mean,

mode, and median. However, the values of mean, mode, and median do provide

us important information about the potential type or shape of the frequency distribution

of the data. Although the shape of the frequency distribution of a data

set could be of any type, most frequently we see the three types of frequency distributions

shown in Figure 18.1.

The location of the measures of centrality as shown in Figure 18.1 provide

the information about the type of data. A data set is symmetric when the values

in the data set that lie equidistant from the mean, on either side, occur with equal

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!