The key is the use of statistically derived random sampling procedures. These ensure that survey results can be defended as statistically representative of the population. Surveys that do not follow these procedures can produce results that lead to misguided market research, strategic, or policy decisions. Any so-called "survey" in which no attempt is made to randomly select respondents, such as call-in readers' or viewers' "polls", is likely to produce results that in no way reflect overall public opinion--even if many thousands of individuals participate. It is true that sampling randomly will eliminate systematic bias The mathematical theorems which justify most frequentist statistical procedures apply only to random samples. http://www.ma.utexas.edu/users/mks/statmistakes/RandomSampleImportance.html no author,

COMMON MISTEAKS MISTAKES IN USING STATISTICS: Spotting and Avoiding Them 4/10/12
Moore and McCabe (2006), Introduction to the Practice of Statistics, Third edition, p 219 Sample Distribution and Sampling Error
Distributions of populations of scores have been discussed. However, a single score does not accurately represent the population. A sample, or subset, of the population is a better estimator of the population. Alternatively, a sample that has received some treatment can be compared to the original population. Just as there is a distribution of scores for a population, there is a distribution of samples (or sampling distribution) for a population. These distributions become perfectly normal when all scores, or all samples, are included. All possible scores/samples are rarely available or possible, but the population can be reasonably represented by proper sampling.******** If the samples are randomly chosen, they are likely to be more representative of the population than a single score is. In addition, the larger the random sample is, the better the representation will be. The sample will likely be different than the population, but the...

...3
Simple RandomSampling
3.1 INTRODUCTION
Everyone mentions simple randomsampling, but few use this method for population-based surveys. Rapid surveys are no exception, since they too use a more complex sampling scheme. So why should we be concerned with simple randomsampling? The main reason is to learn the theory of sampling. Simple randomsampling is the basic selection process of sampling and is easiest to understand. If everyone in a population could be included in a survey, the analysis featured in this book would be very simple. The average value for equal interval and binomial variables, respectively, could easily be derived using Formulas 2.1 and 2.3 in Chapter 2. Instead of estimating the two forms of average values in the population, they would be measuring directly. Of course, when measuring everyone in a population, the true value is known; thus there is no need for confidence intervals. After all the purpose of the confidence interval is to tell how certain the author is that a presented interval brackets the true value in the population. With everyone measured, the true value would be known, unless of course there were measurement or calculation errors. When the true value in a population is estimated with a sample of persons, things get more complicated. Rather then just the mean or proportion, we...

...Chapter 7
Sampling and Sampling Distributions
6-1
Learning Objectives
In this chapter, you learn:
The concept of the sampling distribution
To compute probabilities related to the sample
mean and the sample proportion
The importance of the Central Limit Theorem
To distinguish between different survey
sampling methods
To evaluate survey worthiness and survey errors
7-2
Reasons for Drawing a Sample
Selecting a sample is less time-consuming than
selecting every item in the population (census).
Selecting a sample is less costly than selecting
every item in the population.
An analysis of a sample is less cumbersome
and more practical than an analysis of the
entire population.
7-3
A Sampling Process Begins With A
Sampling Frame
The sampling frame is a listing of items that
make up the population
Frames are data sources such as population
lists, directories, or maps
Inaccurate or biased results can result if a
frame excludes certain portions of the
population
Using different frames to generate data can
lead to dissimilar conclusions
7-4
Types of Samples Used
Nonprobability Sample
Items included are chosen without regard to
their probability of occurrence
Probability Sample
Items in the sample are chosen on the basis
of known probabilities
7-5
Types of Samples Used
(continued)
Samples
Non-Probability
Samples
Judgement
Quota
Chunk...

...SAMPLINGSAMPLING
SAMPLING DISTRIBUTION
(THEORETICAL)
SAMPLING TECHNIQUES (APPLIED)
8/13/2014
QM_Session 14 15
SAMPLING TERMS
An unit/element is the entity on which data are collected.
A population is a collection of all the units/elements of
interest.
A sample is a subset of the population.
The sampled population is the population from
which the sample is drawn.
A frame is a list of the elements/units that the sample will
be selected from.
8/13/2014
QM_Session 14 15
Parameter and Statistic
Parameter is a
population
characteristic
Eg. µ , P, σ
Statistic is a sample
characteristic
Eg. x , s, p
Using Sample
• Statistical Inference:
On basis of sample statistics
derived from limited and
incomplete sample
information
Predict and forecast values of
population parameters...
Estimate and test hypotheses
about values of population
parameters...
Make decisions...
Make generalizations
about the
characteristics of a
population...
8/13/2014
On the basis of
observations of a
sample, a part of a
population
QM_Session 14 15
Selecting a Sample
Sampling from a Finite Population
Sampling from an Infinite Population
8/13/2014
QM_Session 14 15
Sampling from a Finite Population
Finite populations are often defined by lists such as:
Organization membership roster
Credit card account numbers
Inventory product numbers
A simple...

...Application of sampling distribution
Joe Greene, a new manager at Pilgrim Bank wants to better understand profitability data for bank’s customers. Joe is able to obtain a random sample of 31,634 customers on the following variables – Profitability (in $, for the most recent completed year, i.e. 2006), whether or not the customer uses the online banking channel, customer tenure, age and income where available, as well as the customer’s residential area. Descriptive statistics for Profits indicates that the average profit per customer is $111.50 with a standard deviation of $272.84.
a. Is Joe justified in assuming that this is a “large” sample? (see slide 7-14)
YES, BECAUSE 31,634 IS A LOT MORE THAN 30 OBVERSATIONS. GENERALLY, THE LARGER THE SAMPLE, THE MORE RELIABLE ARE THE ESTIMATES. THE KEY IS TO HAVE A RANDOMLY SELECTED SAMPLE TO REDUCE THE RISK OF BIASED ESTIMATES
b. Joe has been informed that the bank serves approximately 5 million customers nationwide – should he worry about using finite population correction factor (slide 7-9).
FINITE POPULATION CORRECTION (FPC) IS NOT NECESSARY, SINCE THE POPULATION OF APPROXIMATELY 5 MILLION IS QUITE LARGE. FPC IS ONLY RECOMMENDED FOR SMALL POPULATIONS.
c. Joe wants to estimate average profit for the entire population based on his sample. He knows that the “point estimate” for average profit would be $111.50, but, he will need to calculate the margin of error. The first step...

...Population and Sampling
MTH/231
August 29, 2012
Importance of Population and Sampling
History from Political Arithmetic to Statistics
The history timeline show evidence of statistical data as early as Ancient Greece time but records show statistics in late 16th century, when it was introduced by, John Graunt, William Petty, and Pascal and later in 17th century by Gottfried Achenwall. It was an exciting time when success and discoveries raised the confidence of scientists, physicist and astronomers to think that laws of nature are not of divine intervention. As the time evolved and new discoveries were attained from political arithmetic like, mortality demographics, census data, economy, and International Statistical Congresses, they all led to changing its name to ‘statistics’.
Population
Every 10 years the country conducts a census of population to provide data that can be of use for research, business marketing, planning, surveys, and different sampling. The first U.S. census took place in 1790. What is ‘population’? The common term “population” describes people that live in a town which is located in a certain region within a certain county or state and their respective characteristic such age, sex, ethnicity, marital status, or other. The statistic term
“population” consist of all members, elements of the defined group. It includes all subjects to be studied or collecting information on for data driven...

...Population and Sampling
MTH/231
Fahad M. Gohar
Statistical data dates back to as early as Ancient Greek time, where it was introduced by John Graunt, William Petty and Pascal in the 16th century. It was then re-introduced by Gottfriend Achenwall in the 17th century. This was a very exciting time for scientists, astronomers and physicists alike as it raised the confidence and knowing that the laws of nature were not of divine intervention. As the years went on, new mathematical discoveries were made such as census data, economy, mortality demographics, and the International Statistical Congresses, which all led to changing its name to “statistics”.
Population
Every decade the US government conducts a census on the population. The data provided in this census is then used for reseach purposes, business marketing, planning, and various other sampling needs. This leads to the question of “What is population?” This can be defined as people that occupy a town which is located in specific region within a specific county/state, and their individual characteristic such as sex, age, ethnicity or marital status. The term “population” is made up of all members and/or elements in that defined group. The basic topics covered in population are birth, growth, age and death.
The statistic term
Sample
In...

...SAMPLING DISTRIBUTIONS
|6.1 POPULATION AND SAMPLING DISTRIBUTION |
|6.1.1 Population Distribution |
Suppose there are only five students in an advanced statistics class and the midterm scores of these five students are:
70 78 80 80 95
Let x denote the score of a student.
• Mean for Population
Based on Example 1, to calculate mean for population:
[pic]
• Standard Deviation for Population
Based on example 1, to calculate standard deviation for population:
[pic]
|6.1.2 Sampling Distribution |
▪ Sample statistic such as median, mode, mean and standard deviation
6.1.2.1 The Sampling Distribution of the Sample Mean
Reconsider the population of midterm scores of five students given in example 1. Let say we draw all possible samples of three numbers each and compute the mean.
Total number of samples = 5C3 =[pic]
Suppose we assign the letters A, B, C, D and E to scores of the five students, so that
A =...

...
Sampling and Data Collection Plan
Name
QNT/561
October 27, 2014
Instructor
Introduction
Royal Blue Airlines is a medium sized airline company offering flights throughout the United States, Mexico, Caribbean Islands, and Latin America. The company operates a fleet of Boeing 737 aircrafts and is in the process of replacing older ones with newer, state-of-the-art planes. These new planes are very expensive, so management wants to maximize passenger count. A study has been authorized to determine: Is there is a difference in the number of passengers taking flights (DV) that are based upon certain days of the week (IV)?
Population and Size
The population for this study consists of airline passengers that numbers in the millions. This population is a vast number of subjects and unrealistic to gather data on each one. The target population will be chosen, and inferences will be made about how the results also apply to the entire population.
Target Population
By narrowing the research to just passengers on Royal Blue Airlines, the study becomes more manageable. Royal Blue Airlines stores data on each flight so they have already had a head start on determining customer trends. By using their company’s data, the cost of the project is drastically reduced and will offer greater insight to answer the research question.
Sampling Element
A survey consisting of six questions (Appendix A) will be handed out to all passengers during...