- The document discusses key concepts related to probability and sampling, including sampling distributions, the central limit theorem, and standard error.
- As sample size increases, the sampling distribution becomes more normal in shape and less variable, with a standard deviation that approaches the population standard deviation divided by the square root of the sample size.
- The central limit theorem states that for large sample sizes, the distribution of sample means will approximate a normal distribution, even if the population is not normally distributed. This allows probabilities to be calculated for sample means.
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Chapter 6: Normal Probability Distribution
6.4: The Central Limit Theorem
Lecture 5 Sampling distribution of sample mean.pptxshakirRahman10
Objectives:
Distinguish between the distribution of population and distribution of its sample means
Explain the importance of central limit
theorem
Compute and interpret the standard error of the mean.
Sampling distribution of
sample mean:
A population is a collection or a set of measurements of interest to the researcher. For example a researcher may be interested in studying the income of households in Karachi. The measurement of interest is income of each household in Karachi and the population is a list of all households in Karachi and their incomes.
Any subset of the population is called a sample from the population. A sample of ‘n’ measurements selected from a population is said to be a random sample if every different sample of size ‘n’ from the population is equally likelyto be selected.
For the purpose of estimation of certain characteristics in the population we would like to select a random sample to be a good representative of the population.
The set of measurements in the population may be summarized by a descriptive characteristic, called a parameter. In the above example the average income of households would be the parameter.
The set of measurements in a sample may be summarized by a descriptive statistic, called a statistic . For example to estimate the average household income in Karachi, we take a random sample of the population in Karachi. The sample mean is a statistic and is an estimate of the population mean.
Because no one sample is exactly like the next , the sample mean will vary from sample to sample ,and hence is itself a random variable.
Random variables have distribution ,and since the sample mean is a random variable it must have a distribution.
If the sample mean has a normal distribution ,we can compute probabilities for specific events using the properties of the normal distribution.
Consider the population with population mean = μ
and standard deviation = σ.
Next, we take many samples of size n, calculate the mean for each one of them, and create a distribution of the sample means.
This distribution is called the Sampling Distribution of Means.
Technically, a sampling distribution of a statistic is the distribution of values of the statistic in all possible samples of the same size from the same population.
Standard error of the
mean:
The quantity σ is referred to as the standard deviation .it is a measure of spread in the population .
The quality σ/n is referred to as the standard error of the sample mean .It is a measure of spread in the distribution of mean
A very important result of statistics referring to the sampling distribution of the sample mean is the Central Limit Theorem .
Central Limit Theorem:
Consider a population with finite mean and standard deviation . If random samples of n measurements are repeatedly drawn from the population then, when n is large, the relative frequency histogram for the sample means ( calculated from repeated samples)
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Chapter 6: Normal Probability Distribution
6.3: Sampling Distributions and Estimators
Vaccine management system project report documentation..pdfKamal Acharya
The Division of Vaccine and Immunization is facing increasing difficulty monitoring vaccines and other commodities distribution once they have been distributed from the national stores. With the introduction of new vaccines, more challenges have been anticipated with this additions posing serious threat to the already over strained vaccine supply chain system in Kenya.
Overview of the fundamental roles in Hydropower generation and the components involved in wider Electrical Engineering.
This paper presents the design and construction of hydroelectric dams from the hydrologist’s survey of the valley before construction, all aspects and involved disciplines, fluid dynamics, structural engineering, generation and mains frequency regulation to the very transmission of power through the network in the United Kingdom.
Author: Robbie Edward Sayers
Collaborators and co editors: Charlie Sims and Connor Healey.
(C) 2024 Robbie E. Sayers
Courier management system project report.pdfKamal Acharya
It is now-a-days very important for the people to send or receive articles like imported furniture, electronic items, gifts, business goods and the like. People depend vastly on different transport systems which mostly use the manual way of receiving and delivering the articles. There is no way to track the articles till they are received and there is no way to let the customer know what happened in transit, once he booked some articles. In such a situation, we need a system which completely computerizes the cargo activities including time to time tracking of the articles sent. This need is fulfilled by Courier Management System software which is online software for the cargo management people that enables them to receive the goods from a source and send them to a required destination and track their status from time to time.
COLLEGE BUS MANAGEMENT SYSTEM PROJECT REPORT.pdfKamal Acharya
The College Bus Management system is completely developed by Visual Basic .NET Version. The application is connect with most secured database language MS SQL Server. The application is develop by using best combination of front-end and back-end languages. The application is totally design like flat user interface. This flat user interface is more attractive user interface in 2017. The application is gives more important to the system functionality. The application is to manage the student’s details, driver’s details, bus details, bus route details, bus fees details and more. The application has only one unit for admin. The admin can manage the entire application. The admin can login into the application by using username and password of the admin. The application is develop for big and small colleges. It is more user friendly for non-computer person. Even they can easily learn how to manage the application within hours. The application is more secure by the admin. The system will give an effective output for the VB.Net and SQL Server given as input to the system. The compiled java program given as input to the system, after scanning the program will generate different reports. The application generates the report for users. The admin can view and download the report of the data. The application deliver the excel format reports. Because, excel formatted reports is very easy to understand the income and expense of the college bus. This application is mainly develop for windows operating system users. In 2017, 73% of people enterprises are using windows operating system. So the application will easily install for all the windows operating system users. The application-developed size is very low. The application consumes very low space in disk. Therefore, the user can allocate very minimum local disk space for this application.
Welcome to WIPAC Monthly the magazine brought to you by the LinkedIn Group Water Industry Process Automation & Control.
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Sachpazis:Terzaghi Bearing Capacity Estimation in simple terms with Calculati...Dr.Costas Sachpazis
Terzaghi's soil bearing capacity theory, developed by Karl Terzaghi, is a fundamental principle in geotechnical engineering used to determine the bearing capacity of shallow foundations. This theory provides a method to calculate the ultimate bearing capacity of soil, which is the maximum load per unit area that the soil can support without undergoing shear failure. The Calculation HTML Code included.
3. - getting a certain type of individual when we
sample once
- getting a certain type of sample mean when n>1
When we take a sample from a population we can talk
about the probability of
today
last Thursday
4. p(X > 50) = ?
10 20 30 40 50 60
1
2
3
frequency 4
5
6
rawscore
70
Distribution of Individuals in a Population
5. 10 20 30 40 50 60
1
2
3
frequency 4
5
6
rawscore
70
p(X > 50) =
1
9
= 0.11
Distribution of Individuals in a Population
6. p(X > 30) = ?
10 20 30 40 50 60
1
2
3
frequency 4
5
6
rawscore
70
Distribution of Individuals in a Population
7. p(X > 30) =
6
9
= 0.66
10 20 30 40 50 60
1
2
3
frequency 4
5
6
rawscore
70
Distribution of Individuals in a Population
8. 10 20 30 40 50 60
1
2
3
frequency 4
5
6
70
normally distributed
µ = 40, σ = 10
Distribution of Individuals in a Population
p(40 < X < 60) = ?
9. 10 20 30 40 50 60
1
2
3
frequency 4
5
6
70
normally distributed
µ = 40, σ = 10
p(40 < X < 60) = p(0 < Z < 2) = 47.7%
Distribution of Individuals in a Population
10. 10 20 30 40 50 60
1
2
3
frequency 4
5
6
70
normally distributed
µ = 40, σ = 10
rawscore
Distribution of Individuals in a Population
p(X > 60) = ?
11. 10 20 30 40 50 60
1
2
3
frequency 4
5
6
rawscore70
normally distributed
µ = 40, σ = 10
p(X > 60) = p(Z > 2) = 2.3%
Distribution of Individuals in a Population
12. For the preceding calculations to be accurate, it is
necessary that the sampling process be random.
A random sample must satisfy two requirements:
1. Each individual in the population has an equal
chance of being selected.
2. If more than one individual is to be selected, there
must be constant probability for each and every
selection (i.e. sampling with replacement).
13. A distribution of sample means is:
the collection of sample means for all the possible
random samples of a particular size (n) that can be
obtained from a population.
Distribution of Sample Means
15. Distribution of Sample Means
from Samples of Size n = 2
1 2, 2 2
2 2,4 3
3 2,6 4
4 2,8 5
5 4,2 3
6 4,4 4
7 4,6 5
8 4,8 6
9 6,2 4
10 6,4 5
11 6,6 6
12 6,8 7
13 8,2 5
14 8,4 6
15 8.6 7
16 8.8 8
Sample # Scores Mean ( )X
16. Distribution of Sample Means
from Samples of Size n = 2
1 2 3 4 5 6
1
2
3
frequency 4
5
6
7 8 9
sample mean
We can use the distribution of sample means to answer
probability questions about sample means
17. Distribution of Sample Means
from Samples of Size n = 2
1 2 3 4 5 6
1
2
3
frequency 4
5
6
7 8 9
sample mean
p( > 7) = ?X
18. Distribution of Sample Means
from Samples of Size n = 2
1 2 3 4 5 6
1
2
3
frequency 4
5
6
7 8 9
sample mean
p( > 7) = 1
16
= 6 %X
19. 1 2 3 4 5 6
1
2
3
frequency
4
5
6
rawscore
7 8 9
Distribution of Individuals in Population
Distribution of Sample Means
1 2 3 4 5 6
1
2
3
frequency
4
5
6
7 8 9
sample mean
µ = 5, σ = 2.24
µX = 5, σX = 1.58
20. 1 2 3 4 5 6
1
2
3
frequency
4
5
6
rawscore
7 8 9
1 2 3 4 5 6
1
2
3
frequency
4
5
6
7 8 9
sample mean
Distribution of Individuals
Distribution of Sample Means
µ = 5, σ = 2.24
p(X > 7) = 25%
µX = 5, σX = 1.58
p(X> 7) = 6% , for n=2
21. A key distinction
Population Distribution – distribution of all individual scores
in the population
Sample Distribution – distribution of all the scores in your
sample
Sampling Distribution – distribution of all the possible sample
means when taking samples of size n from the population. Also
called “the distribution of sample means”.
22. 1 2 3 4 5 6
1
2
3
frequency
4
5
6
rawscore
7 8 9
Distribution of Individuals in Population
Distribution of Sample Means
1 2 3 4 5 6
1
2
3
frequency
4
5
6
7 8 9
sample mean
µ = 5, σ = 2.24
µX = 5, σX = 1.58
23. 1 2 3 4 5 6
1
2
3
frequency
4
5
6
7 8 9
sample mean
Distribution of Sample Means
Things to Notice
1. The sample means tend to pile up
around the population mean.
2. The distribution of sample means is
approximately normal in shape, even
though the population distribution was
not.
3. The distribution of sample means has
less variability than does the population
distribution.
25. Distribution of Sample Means
from Samples of Size n = 3
1 2 3 4 5 6
2
4
6
frequency
8
10
12
7 8 9
sample mean
14
16
18
20
22
24
1
64
= 2 %
µX = 5, σX = 1.29
p( X > 7) =
26. Distribution of Sample Means
As the sample gets bigger, the
sampling distribution…
1. stays centered at the population
mean.
2. becomes less variable.
3. becomes more normal.
27. Central Limit Theorem
For any population with mean µ and standard deviation σ,
the distribution of sample means for sample size n …
1. will have a mean of µ
2. will have a standard deviation of
3. will approach a normal distribution as
n approaches infinity
σ
n
28. Notation
the mean of the sampling distribution
the standard deviation of sampling distribution
(“standard error of the mean”)
µµ =X
n
X
σ
σ =
29. The “standard error” of the mean is:
The standard deviation of the distribution of sample
means.
The standard error measures the standard amount of
difference between x-bar and µ that is reasonable to
expect simply by chance.
Standard Error
SE =
σ
n
30. The Law of Large Numbers states:
The larger the sample size, the smaller the standard
error.
Standard Error
This makes sense from the formula for
standard error …
31. 1 2 3 4 5 6
1
2
3
frequency
4
5
6
rawscore
7 8 9
Distribution of Individuals in Population
Distribution of Sample Means
1 2 3 4 5 6
1
2
3
frequency
4
5
6
7 8 9
sample mean
µ = 5, σ = 2.24
µX = 5, σX = 1.58
58.1
2
24.2
==X
σ
34. Central Limit Theorem
For any population with mean µ and standard deviation σ,
the distribution of sample means for sample size n …
1. will have a mean of µ
2. will have a standard deviation of
3. will approach a normal distribution as
n approaches infinity
σ
n
What does this mean in
practice?
35. Practical Rules Commonly Used:
1. For samples of size n larger than 30, the distribution of the sample
means can be approximated reasonably well by a normal distribution.
The approximation gets better as the sample size n becomes larger.
2. If the original population is itself normally distributed, then the sample
means will be normally distributed for any sample size.
small n large n
normal population
non-normal population
normalisX normalisX
normalisXnonnormalisX
36. Probability and the Distribution of Sample
Means
The primary use of the distribution of sample
means is to find the probability associated with any
specific sample.
37. Probability and the Distribution of Sample
Means
Given the population of women has normally
distributed weights with a mean of 143 lbs and
a standard deviation of 29 lbs,
Example:
1. if one woman is randomly selected, find the probability that her
weight is greater than 150 lbs.
2. if 36 different women are randomly selected, find the probability
that their mean weight is greater than 150 lbs.
38. 0 0.24
Given the population of women has normally distributed
weights with a mean of 143 lbs and a standard deviation of
29 lbs,
1. if one woman is randomly selected, find the probability that her
weight is greater than 150 lbs.
0.4052
150µ = 143
σ = 29
Population distribution
z = 150-143 = 0.24
29
39. 0 1.45
Given the population of women has normally distributed
weights with a mean of 143 lbs and a standard deviation of
29 lbs,
0.0735
2. if 36 different women are randomly selected, find the probability
that their mean weight is greater than 150 lbs.
36
29
=X
σ
150µ = 143
σ = 4.33
Sampling distribution
z = 150-143 = 1.45
4.33
40. Probability and the Distribution of Sample
Means
Given the population of women has normally
distributed weights with a mean of 143 lbs and
a standard deviation of 29 lbs,
Example:
1. if one woman is randomly selected, find the probability that her
weight is greater than 150 lbs.
2. if 36 different women are randomly selected, find the probability
that their mean weight is greater than 150 lbs.
41.)150( =>XP
07.)150( =>XP
41. Practice
Given a population of 400 automobile models,
with a mean horsepower = 105 HP, and a
standard deviation = 40 HP,
Example:
1. What is the standard error of the sample mean for a sample of
size 1?
2. What is the standard error of the sample mean for a sample of
size 4?
3. What is the standard error of the sample mean for a sample of
size 25?
40
20
8
42. Example:
1. if one model is randomly selected from the population, find the
probability that its horsepower is greater than 120.
2. If 4 models are randomly selected from the population, find the
probability that their mean horsepower is greater than 120
3. If 25 models are randomly selected from the population, find the
probability that their mean horsepower is greater than 120
Practice
Given a population of 400 automobile models,
with a mean horsepower = 105 HP, and a
standard deviation = 40 HP,
.35
.23
.03