Wikipedia
random samples : A sample is a subject chosen from a population for investigation. A random sample is one chosen by a method involving an unpredictable component. Random sampling can also refer to taking a number of independent observations from the same probability distribution, without involving any real population. A probability sample is one in which each item has a known probability of being in the sample. The sample usually will not be completely representative of the population from which it was drawn— this random variation in the results is known as sampling error. In the case of random samples, mathematical theory is available to assess the sampling error. Thus, estimates obtained from random samples can be accompanied by measures of the uncertainty associated with the estimate. This can take the form of a standard error, or if the sample is large enough for the central limit theorem to take effect, confidence intervals may be calculated. Random sampling- all members of the populatio.... More from Wikipedia
random samples : In statistics, a simple random sample is a subset of individuals (a sample) chosen from a larger set (a population). Each individual is chosen randomly and entirely by chance, such that each individual has the same probability of being chosen at any stage during the sampling process, and.. More from Wikipedia
Random Experiment and Sample Space
Random Experiment and Sample Space - An experiment repeated under essentially homogeneous and similar conditions results in an outcome, which is unique or not unique but may be one of the several possible outcomes. When the result is unique then the experiment is called a 'deter..
Random Experiment and Sample Space
An experiment repeated under essentially homogeneous and similar conditions results in an outcome, which is unique or not unique but may be one of the several possible outcomes. When the result is unique then the experiment is called a 'deterministic' experime..
Google Tech Talks August 17, 2006 Ziv Bar-Yossef joined Google from the Technion - Israel Institute of Technology in Haifa, Israel. He received his PhD from UC Berkeley in 2002, and was a Research Staff Member at the IBM Almaden Research Center prior to joining Technion. This was an academic study conducted before Ziv Bar-Yossef joined Google and does not represent Google's views. ABSTRACT We revisit a problem introduced by Bharat and Broder almost a decade ago: how to sample random pages ...
Recorded on September 30, 2008 using a Flip Video camcorder.
Question : Time spent using e-mail per session is normally distributed with mean of 8 minutes and standard deviation of 2 minutes. If you select a random sample of 25 sessions
a)What is the probability that the sample mean is between 7.8 and 8.2 minutes?
b)What is the probability that the sample mean is between 7.5 and 8 minutes
c)If you select a random sample of 100 sessions what is the probability that the sample mean is between 7.8 and 8.2 minutes
Answer : These are all done in essentially the same way. I will solve (a). Key fact: (xbar - )/( / n) has standard normal distribution, where xbar is the sample mean, is the population mean, is the population standard deviation, and n is the sample size. P(7.8 < xbar < 8.2) = P( (7.8 - 8.0)/(2/ 25) < (xbar - 8.0)/(2/ 25) < (8.2 - 8.0)/(2/ 25) ) = P(-0.5 < (xbar - 8.0)/(2/ 25) < 0.5) = N_z(0.5) - N_z(-0.5) = 0.6915 - 0.3085 = 0.3830 The other two are solved very similarly. You should get 0.3944 for (b) and 0.6826 for (c).. More from Yahoo Answers
Answer : These are all done in essentially the same way. I will solve (a). Key fact: (xbar - )/( / n) has standard normal distribution, where xbar is the sample mean, is the population mean, is the population standard deviation, and n is the sample size. P(7.8 < xbar < 8.2) = P( (7.8 - 8.0)/(2/ 25) < (xbar - 8.0)/(2/ 25) < (8.2 - 8.0)/(2/ 25) ) = P(-0.5 < (xbar - 8.0)/(2/ 25) < 0.5) = N_z(0.5) - N_z(-0.5) = 0.6915 - 0.3085 = 0.3830 The other two are solved very similarly. You should get 0.3944 for (b) and 0.6826 for (c).. More from Yahoo Answers
Question : Here is a link to the question:
http://farm3.static.flickr.com/2021/2260865217_587efbd43c_o.jpg
Thanks!
Answer : The formula for test statistic is (xbar - ) / sample standard deviation Plug in 190 for xbar, 200 for , and 47 for sample standard deviation. (190-200)/47 = -0.213 And your level of significance is 0.03. The z-score associated with p=0.03 is about -1.9. That means for this level of significance, to reject your null hypothesis based on the sample, the sample would have to produce a test statistic at least as extreme as -1.9 (in other words, less than or equal to -1.9). -0.213 isn't even close to that small, so you can't reject the null hypothesis. The correct answer is F. You cannot reject the null because z is not less than -1.9... More from Yahoo Answers
Answer : The formula for test statistic is (xbar - ) / sample standard deviation Plug in 190 for xbar, 200 for , and 47 for sample standard deviation. (190-200)/47 = -0.213 And your level of significance is 0.03. The z-score associated with p=0.03 is about -1.9. That means for this level of significance, to reject your null hypothesis based on the sample, the sample would have to produce a test statistic at least as extreme as -1.9 (in other words, less than or equal to -1.9). -0.213 isn't even close to that small, so you can't reject the null hypothesis. The correct answer is F. You cannot reject the null because z is not less than -1.9... More from Yahoo Answers
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