Lecture 5 Understanding of Techniques to Analyse Date Effectively

Tutor: Teenanda Ayasamy

Collect data : e.g. Survey

Present data: e.g. Tables and graphs

Characterize data: e.g. The sample mean

Estimation

e.g., Estimate the population

mean weight using the sample

mean weight

Hypothesis testing

e.g., Test the claim that the

population mean weight is 120

pounds

Drawing conclusions about a large group of individuals based on a smaller group.

VARIABLES Variables are a characteristics of an item or individual and are what you analyze when you use a statistical method.

DATA Data are the different values associated with a variable.

OPERATIONAL DEFINITIONS Data values are meaningless unless their variables have operational definitions, universally accepted meanings that are clear to all associated with an analysis.

POPULATION A population consists of all the items or individuals about which you want to draw a conclusion. The population is the “large group”

SAMPLE A sample is the portion of a population selected for analysis. The sample is the “small group”

PARAMETER A parameter is a numerical measure that describes a characteristic of a population.

STATISTIC A statistic is a numerical measure that describes a characteristic of a sample.

Population Sample

Measures used to describe the

population are called parameters

Measures used to describe the

sample are called statistics

Using the DCOVA methodology

Define the variables for which you want to reach conclusions

Collect the data from appropriate sources

Organize the data collected by developing tables

Visualize the data by developing charts

Analyze the data by examining the appropriate tables and charts (and in later chapters by using other statistical methods) to reach conclusions

Variables

Categorical

Numerical

Discrete Continuous

Examples:

Marital Status

Political Party

Eye Color

(Defined categories)

Examples:

Number of Children

Defects per hour

(Counted items)

Examples:

Weight

Voltage

(Measured

characteristics)

DCOVA Categorical (qualitative)

variables have values that can only be placed into categories, such as “yes” and “no.”

Numerical (quantitative) variables have values that represent quantities. o Discrete variables arise from a

counting process

o Continuous variables arise from a measuring process

Primary Sources: The data collector is the one using the data for analysis

o Data from a political survey

o Data collected from an experiment

o Observed data

Secondary Sources: The person performing data analysis is not the data collector

o Analyzing census data

o Examining data from print journals or data published on the internet.

Sources of data fall into four categories

Data distributed by an organization or an individual

A designed experiment

A survey

An observational study

DCOVA

Sort raw data in ascending order:

12, 13, 17, 21, 24, 24, 26, 27, 27, 30, 32, 35, 37, 38, 41, 43, 44, 46, 53, 58

Find range: 58 - 12 = 46

Select number of classes: 5 (usually between 5 and 15)

Compute class interval (width): 10 (46/5 then round up)

Determine class boundaries (limits): Class 1: 10 to less than 20 Class 2: 20 to less than 30 Class 3: 30 to less than 40 Class 4: 40 to less than 50 Class 5: 50 to less than 60

Compute class midpoints: 15, 25, 35, 45, 55

Count observations & assign to classes

DCOVA

Class Midpoints Frequency

10 but less than 20 15 3





Total 20

Data in ordered array:

12, 13, 17, 21, 24, 24, 26, 27, 27, 30, 32, 35, 37, 38, 41, 43, 44, 46, 53, 58

DCOVA

Class Frequency

10 but less than 20 3 .15 15

20 but less than 30 6 .30 30

30 but less than 40 5 .25 25

40 but less than 50 4 .20 20

50 but less than 60 2 .10 10

Total 20 1.00 100

Relative

Frequency Percentage


12, 13, 17, 21, 24, 24, 26, 27, 27, 30, 32, 35, 37, 38, 41, 43, 44, 46, 53, 58

DCOVA

Class

10 but less than 20 3 15% 3 15%

20 but less than 30 6 30% 9 45%

30 but less than 40 5 25% 14 70%

40 but less than 50 4 20% 18 90%

50 but less than 60 2 10% 20 100%

Total 20 100 20 100%

Percentage Cumulative Percentage


12, 13, 17, 21, 24, 24, 26, 27, 27, 30, 32, 35, 37, 38, 41, 43, 44, 46, 53, 58

Frequency Cumulative

Frequency

DCOVA

It condenses the raw data into a more useful form

It allows for a quick visual interpretation of the data

It enables the determination of the major characteristics of the data set including where the data are concentrated / clustered

Frequency Distributions: Some Tips

Different class boundaries may provide different pictures for the same data (especially for smaller data sets)

Shifts in data concentration may show up when different class boundaries are chosen

As the size of the data set increases, the impact of alterations in the selection of class boundaries is greatly reduced

When comparing two or more groups with different sample sizes, you must use either a relative frequency or a percentage distribution

DCOVA

In a bar chart, a bar shows each category, the length of which

represents the amount, frequency or percentage of values falling into a

category which come from the summary table of the variable.

Banking Preference? %

ATM 16%

Automated or live

telephone

2%

Drive-through service at

branch

17%

In person at branch 41%

Internet 24%

Banking Preference

0% 5% 10% 15% 20% 25% 30% 35% 40% 45%

ATM

Automated or live telephone

Drive-through service at branch

In person at branch

Internet

DCOVA

The pie chart is a circle broken up into slices that represent categories. The

size of each slice of the pie varies according to the percentage in each

category.

Banking Preference

16%

2%

17%

41%

24%

ATM

Automated or live

telephone


branch

In person at branch

Internet

DCOVA

Banking Preference? %

ATM 16%

Automated or live

telephone

2%


branch

17%

In person at branch 41%

Internet 24%

A vertical bar chart of the data in a frequency distribution is called a histogram.

In a histogram there are no gaps between adjacent bars.

The class boundaries (or class midpoints) are shown on the horizontal axis.

The vertical axis is either frequency, relative frequency, or percentage.

The height of the bars represent the frequency, relative frequency, or percentage.

DCOVA

Class Frequency

10 but less than 20 3 .15 15

20 but less than 30 6 .30 30

30 but less than 40 5 .25 25

40 but less than 50 4 .20 20

50 but less than 60 2 .10 10

Total 20 1.00 100

Relative

Frequency Percentage

0

2

4

6

8

5 15 25 35 45 55 More

Fre

qu

en

cy

Histogram: Age Of Students

(In a percentage histogram the vertical axis would be

defined to show the percentage of observations per

class)

A percentage polygon is formed by having the midpoint of each

class represent the data in that class and then connecting the

sequence of midpoints at their respective class percentages.

The cumulative percentage polygon, or ogive, displays the

variable of interest along the X axis, and the cumulative

percentages along the Y axis.

Useful when there are two or more groups to compare.

DCOVA

2-

18

01234567

5 15 25 35 45 55 65

Fre

quen

cy

Frequency Polygon: Age Of Students

Class Midpoints

Class






Frequency Class

Midpoint

(In a percentage polygon the

vertical axis would be defined to

show the percentage of

observations per class)

DCOVA

0

20

40

60

80

100

10 20 30 40 50 60

Cu

mu

lati

ve P

erc

en

tage

Ogive: Age Of Students

Class






% less

than lower

boundary

Lower class

boundary

Lower Class Boundary

(In an ogive the percentage of the

observations less than each lower

class boundary are plotted versus the

lower class boundaries.

DCOVA

Scatter plots are used for numerical data consisting of paired observations taken from two numerical variables

One variable is measured on the vertical axis and the other variable is measured on the horizontal axis

Scatter plots are used to examine possible relationships between two numerical variables

DCOVA

Volume

per day

Cost per

day

23 125

26 140

29 146

33 160

38 167

42 170

50 188

55 195

60 200

Cost per Day vs. Production Volume

0

50

100

150

200

250

20 30 40 50 60 70

Volume per Day

Co

st

per

Day

DCOVA

Lecture 5 Understanding of Techniques to Analyse Date Effectively

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Transcript of Lecture 5 Understanding of Techniques to Analyse Date Effectively