Types of Sampling Essay Example for Free

Types of Sampling Essay * How do we decide which to use? * How do we analyze the results differently depending on the type of sampling? Non-probability Sampling: Why dont we use non-probability sampling schemes? Two reasons: * We cant use the mathematics of probability to analyze the results. * In general, we cant count on a non-probability sampling scheme to produce representative samples. In mathematical statistics books (for courses that assume you have already taken a probability course): * Described as assumptions about random variables * Sampling with replacement versus sampling without replacement What are the main types of sampling and how is each done? Simple Random Sampling: A simple random sample (SRS) of size n is produced by a scheme which ensures that each subgroup of the population of size n has an equal probability of being chosen as the sample. Stratified Random Sampling: Divide the population into strata. There can be any number of these. Then choose a simple random sample from each stratum. Combine those into the overall sample. That is a stratified random sample. (Example: Church A has 600 women and 400 women as members. One way to get a stratified random sample of size 30 is to take a SRS of 18 women from the 600 women and another SRS of 12 men from the 400 men.) Multi-Stage Sampling: Sometimes the population is too large and scattered for it to be practical to make a list of the entire population from which to draw a SRS. For instance, when the a polling organization samples US voters, they do not do a SRS. Since voter lists are compiled by counties, they might first do a sample of the counties and then sample within the selected counties. This illustrates two stages. In some instances, they might use even more stages. At each stage, they might do a stratified random sample on sex, race, income level, or any other useful variable on which they could get information before sampling. How does one decide which type of sampling to use? The formulas in almost all statistics books assume simple random sampling. Unless you are willing to learn the more complex techniques to analyze the data after it is collected, it is appropriate to use simple random sampling. To learn the appropriate formulas for the more complex sampling schemes, look for a book or course on sampling. Stratified random sampling gives more precise information than simple random sampling for a given sample size. So, if information on all members of the population is available that divides them into strata that seem relevant, stratified sampling will usually be used. If the population is large and enough resources are available, usually one will use multi-stage sampling. In such situations, usually stratified sampling will be done at some stages. How do we analyze the results differently depending on the different type of sampling? The main difference is in the computation of the estimates of the variance (or standard deviation). An excellent book for self-study is A Sampler on Sampling, by Williams, Wiley. In this, you see a rather small population and then a complete derivation and description of the sampling distribution of the sample mean for a particular small sample size. I believe that is accessible for any student who has had an upper-division mathematical statistics course and for some strong students who have had a freshman introductory statistics course. A very simple statement of the conclusion is that the variance of the estimator is smaller if it came from a stratified random sample than from simple random sample of the same size. Since small variance means more precise information from the sample, we see that this is consistent with stratified random sampling giving better estimators for a given sample size. Return to the top. Non-probability sampling schemes These include voluntary response sampling, judgement sampling, convenience sampling, and maybe others. In the early part of the 20th century, many important samples were done that werent based on probability sampling schemes. They led to some memorable mistakes. Look in an introductory statistics text at the discussion of sampling for some interesting examples. The introductory statistics books I usually teach from are Basic Practice of Statistics by David Moore, Freeman, and Introduction to the Practice of  Statistics by Moore and McCabe, also from Freeman. A particularly good book for a discussion of the problems of non-probability sampling is Statistics by Freedman, Pisani, and Purves. The detail is fascinating. Or, ask a statistics teacher to lunch and have them tell you the stories they tell in class. Most of us like to talk about these! Someday when I have time, maybe Ill write some of them here. Mathematically, the important thing to recognize is that the discipline of statistics is based on the mathematics of probability. Thats about random variables. All of our formulas in statistics are based on probabilities in sampling distributions of estimators. To create a sampling distribution of an estimator for a sample size of 30, we must be able to consider all possible samples of size 30 and base our analysis on how likely each individual result is. Return to the top. In mathematical statistics books (for courses that assume you have already taken a probability course) the part of the problem relating to the sampling is described as assumptions about random variables. Mathematical statistics texts almost always says to consider the Xs (or Ys) to be independent with a common distribution. How does this correspond to some description of how to sample from a population? Answer: simple random sampling with replacement. Return to the top. Types of Graphs - Line Graphs Comparing various sets of data can be complicated, but line graphs make it easy. The plotted peaks and dips on the grid allow you to monitor and compare improvement and decline. Scientists use line graphs all the time, as do all types of professionals and students. Learn more about line graphsà ¢Ã¢â€š ¬Ã¢â‚¬ the most popular type of graph. - Bar Graphs Pleasing to the eyes, bar graphs compare data in a simple format consisting of rectangular bars. With a few varieties to choose from, settling on the right bar graph might be confusing. Should you go with a horizontal, vertical, double or group bar graph? Read on to find out. - Pictographs You first encounter pictographs during childhood and bump into them all through lifeà ¢Ã¢â€š ¬Ã¢â‚¬ at school, work, and all over magazines and on TV. These diagrams, which use small picture symbols to compare information, are a media favorite; statisticians, though, do not share the sentiment. Find out why, and learn more about the uses of pictographs. - Pie Charts Simple to make and simple to understand, a pie chart is a popular form of data comparison, consisting of a circle that is split into parts. When should you use pie charts, and when should you not? Learn about their advantages and disadvantages, and get some tips on making pie charts. - Cosmographs A cosmograph is a type of chart that shows comparisons. In doing so, it makes life and work easier. If you want to prepare an input-output model for your organization, or compare the features of a geographical region through a simple visual, cosmographs come in handy. Find out how a cosmograph can help you. - Organizational Charts These diagrams represent the relationships between the different positions and ranks of a company through a series of boxes that go from top to bottom and side to side. Not only does anorganizational chart add order and structure to an organization, but it also shows if changes are needed. Get more information on organizational charts. - Flow Charts When projects seem overbearing and processes seem complex, flow charts can save the day by break things down into smaller steps and giving you a clearer idea of the overall process. Shapes are typically used to represent the components of a flow chart. Find out what these shapes represent and learn more about flow charts.

Poverty in Grapes of Wrath, by John Steinbeck :: Grapes of Wrath Essays

Throughout history, less fortunate people have been set apart or shunned from the general public. In the Grapes of Wrath, by John Steinbeck, this statement holds true. Throughout the whole book, all of the less fortunate people are treated like they aren’t even human. This is not much different than how our society is now. In the news article â€Å"Major Cities Get Tough With Homeless†, by Angie Cannon, Judy Appel said, â€Å"We are saying it is your fault that we have created a structure where there aren’t enough jobs and housing for you to lead a decent life.† (Cannon 1) Appel is saying the same thing Steinbeck was saying in his book. Many homeless people are homeless because they were forced to be that way, and the general public doesn’t realize it. In the Grapes of Wrath, and in the present time, the general public has set the less fortunate apart from themselves without even realizing it. â€Å"I’m seeing more apathy on the part of people. I think people used to feel badly. And now, I think people feel bothered. That’s a dangerous shift.† (Cannon 1) What she means is that at one point in time we used to care for the homeless. We used to try and help them out. Now we don’t care and we just want to get rid of them. This is very similar to the situation in the Grapes of Wrath. At first they wanted thousands of people to come and work, but when they actually started coming, the general public wanted to get rid of them. â€Å"And the men of the towns and of the soft suburban county gathered to defend themselves; and the reassured themselves that they were good and the invaders were bad, as a man must do before he fights. They said, these Okies are dirty and ignorant. They’re degenerate sexual man iacs. These Okies are thieves. They’ll steal anything. They’ve got no sense of property rights.† (G.O.W. 363) This was the general publics’ feeling towards the Okies, even though they asked them to come there in the first place. What the people don’t understand is that the Okies are being forced to steal and the general public is the one who is forcing them. In the Grapes of Wrath, and in the present time we, the general public have shunned the less fortunate. It isn’t that we want them to be poor, but we have a hard time fitting in with them.

Agricultural Production in Ancient Civilizations Essay

During the period of 500 C. E – 1000 C. E. ancient civilizations in North and South America and China cultivated and gradually moved from the hunting and gathering lifestyles. These civilizations drifted towards food collection and then farming. This approach, crops and attitudes toward agriculture varied with culture. With the Native Americans and the Ancient Chinese during 500 C. E – 1000 C. E. have both differences and similarities towards agricultural production. Document 1, tells of a story about how Maria Manuela de Cora (an Inca Author) passes along ancient legends. One that is called â€Å"Seeds† that says that one day the son of the sun kills a child that was made by the sun. The son of the sun got scared of the anger of his father and scattered about the world the pieces of his murdered brother. It tells that his body parts like his teeth grew corn. This would be a story about the creation of corn, why it was there and how. However, document 7 talks of an Ancient Chinese Legend. This talks more about that fact that if you took the weeds you could fertilize the farmer’s crops. With each story tells something to do with farming. How that one, thing is made or how to make their crops better. Document 5, is a diagram of a hunting scene and peasants working in a field in Ancient China. This illustration gave a reason for historians to track the development of tool- and weapon making in organization in agrarian and artisan production as well as the leisure activities of officials and the landed elites. With document 3 talks about Mesoamerican origins. Historians talk about that current archaeological evidence cannot pinpoint a single location where Indian agriculture began or determine precisely why the Indians became agriculturists. They did though have records that suggested that the cultivation and domestication of plants. With the painting and the records gave historians a better view of each hunting scene and peasants working in fields. During the period of 500 C. E – 1000 C. E. ancient civilizations in North and South America and China cultivated and gradually moved from the hunting and gathering lifestyles. These civilizations drifted towards food collection and then farming. With this approach, crops and attitudes toward agriculture varied with culture. With the Native Americans and the Ancient Chinese during 500 C. E – 1000 C. E. have both differences and similarities towards agricultural production. Showing that China was more into the facts then stories like Mesoamerica to explain the reasoning of agricultural in both of China and Native Americans.

Personality Theory on Oprah Winfrey - 761 Words

Any person experiences growth of different aspects of personality during various points of time. In fact, it is the day to day good and bad experiences that shape the personality of an individual. There are different theories of growth of personality of an individual. In this assignment, I will take up the case of well-known figure Oprah Winfrey. Based on different theories of personality, I will study the factors which contributed to the growth of personality of Oprah Winfrey. Experts have worked on the science of personality development. They have presented the various theories of growth of a personality. The term personality is the product of learned behavior. (Bergland)This means that many traits are inborn and many others are†¦show more content†¦She established a foundation to assist women, children and families in the United States and other countries of the world. She encouraged people to contribute to fight against evils in the society by giving importance to charity. (Thomson Gayle) In this section, I will take up two theories of personality development and try to apply them in the case of Oprah Winfrey. In this case, I will take up trait theory and socialShow MoreRelatedEssay on Personality: the Oprah Winfrey Show837 Words   |  4 Pageswell-known current or historical person for an in-depth analysis of personality development. Some examples of the type of person you can choose are famous politicians, philanthropists, entertainers, bus inesspersons, or individuals who made significant contributions to your field of study or career. You should choose a figure whose biographical information can be easily researched. During this course, you have studied several models of personality development. 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