Sujet: variance liste de sujets
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	Sample variance		2010-01-25
		shodhan pose la question : A series of 100 measurements of a physical quantity have been made that show a random fluctions characterized by a sample variance of 2% of teh mean value. If the series is lengthed to 1000 measurements made under the same conditions, estimates the sample variance of the larger set of data. Robert Dawson lui répond.
	The variance		2009-02-09
		Ashley pose la question : what is the varinace of these scoress 53,67,43,54,58,54,47,35,45,56,45,47,54 Harley Weston lui répond.
	Sample variance: inches to centimeters		2008-09-22
		Anita pose la question : The average height of a sample of basketball players is 6 feet, 2 inches or 74 inches. The standard deviation of this sample of players is 4 inches. If each person's height were to be multiplied by 2.54, what would be the value of the resulting sample variance? Harley Weston lui répond.
	The mean and variance		2008-06-05
		Donny pose la question : An investment will be worth $1,000, $2,000, or $5,000 at the end of the year. The probabilities of these values are .25, .60, and .15, respectively. Determine the mean and variance of the worth of the investment. Harley Weston lui répond.
	Expected value and standard deviation		2008-03-19
		Patrick pose la question : Heres a question i cant figure out: a small airline company has only three flights per day. The number of delayed flights per day is regarded as a random variable, and I'm supposed to calculate the expected value and standard deviation of the number of delays. the probability distribution looks like: No. of Delays: 0 1 2 3 Prob. of delay: 05. 0.3 .1 .1 Harley Weston lui répond.
	Grouped data		2007-10-08
		Nimra pose la question : The following sets of data represent the distributions of house prices in the north-east and south-west of a country. Random samples of 100 houses were selected in each region. (a) Calculate the mean, median and standard deviation for Harley Weston lui répond.
	Sample variance and population variance		2007-09-22
		Willy pose la question : I have a question in sample variance and population my name is Willy the question in the attached file... Harley Weston lui répond.
	A statistics example		2007-08-02
		Claudia pose la question : A particular employee arrives to work some time between 8:00 am - 8:30 am. Based on past experience the Company has determined that the employee is equally likely to arrive at any time between 8:00 am - 8:30 am. On average, what time does the employee arrive? What is the standard deviation of the time at which the employee arrives? Find the probability that the employee arrives exactly at 8:12 am? Find the probability that the employee arrives between 8:20 am - 8:25 am? Har lui répond.
	Types of variances		2007-05-08
		Latoay pose la question : my teacher asked me to name two type of vairiance. i feel the answer is population and simple variance but i'm not sure. thank you Stephen La Rocque lui répond.
	Incremental standard deviation		2007-04-28
		Murtaza pose la question : Hi In relation my question asked earlier, i would first like to thank you for the prompt reply. But it has not answered my query yet. Let me frame the problem again. I have a mean value for N data items. (note that i know N but i donot know the distinct N data item values) Now the (N+1)th data item comes in and i calculate the new mean. (incremental method for that is simple). How do i calculate the new standard deviation. The formula you gave me requires me to read the data items once and at the end of the pass i will have have the standard deviation. But i need the STDDEV values at intermediate stages as well. Is it possible ? Murtaza Penny Nom lui répond.
	A one pass calculation of standard deviation		2007-03-19
		Murtaza pose la question : Hi I searched the listings but couldn't find what i am looking for. I have a dataset and i am allowed only 1 pass through it. At the end of this pass i must have the mean and standard deviation. Calculating the mean is easy as also demonstrated in your listings. I think the same can be done for standard deviation as well. But the doubt that i have is this :- Will the calculated standard deviation be sequence dependent ? i.e. if i change the order in which the data items enter the system, will the std deviation also change ?? Thanks in advance Murtaza Penny Nom lui répond.
	Sample variance		2005-08-17
		Rosalie pose la question : To give an unbiased estimate of the population variance, the denominator of the sample variance should be (n-1) instead of n. I tried to convince myself by comparing the population variance and sample variance (with denominator n and n-1): Penny Nom lui répond.
	Standard deviation		2005-01-02
		Urial pose la question : Find the standard deviation of the given data set To get the best deal for CD dealer, Jessica called eight appliance stores and asked the cast of a specific model. The prices she quoted are listed below. $300, $203, $272, $332, $440, $119, $129,$254 Penny Nom lui répond.
	Incremental variance		2004-09-23
		Carlos pose la question : I must keep statistical data (mean and variance) in 3 granularity levels depending on the age of the data (daily for older than 1 year, hourly for older than 1 month and quarter-hour for older than 1 day). How can I calculate the resulting variance from a set of variances previously calculated supposing I have the count and mean for each member of the set? Andrei Volodin and Penny Nom lui répond.
	E(X + Y) and V(X + Y)		2003-07-10
		Reuben pose la question : I'm a teacher trying to find a way to make some stats work from first principles. The topic is expectation algebra and it is for the top age level in high school. By using a set of data I can show how the mean is the same as the expected value ie 2,2,3,4,4 is 15 / 5 = 3 also, 2x0.4+3x0.2+4x0.4=3. I can also show this to work for the variance in the same style but using Sum(x-mean)2/n and the Var(X) version of squaring x then multiplying by the probability ( all this for random independant samples). Now comes the tricky bit.....when I try to show E(X+Y) = E(X) + E(Y) from setting up two data sets I get it to work only if I add each item from X to each item from Y. However, I can't get it to work for V(X+Y)=V(X) + V(Y) from two sets of data. There must be something missing in my knowledge of how the sets are required to add together or my knowledge of expectation algebra. I am familiar with proofs but still want to show my students that the basic formulae work from groups of data whether done the long way or by use of formulae. Can you help please? Penny Nom lui répond.
	Incremental standard deviation		2003-04-12
		Carlos pose la question : I need to calculate the standard deviation for a group of data, but I don't know in advance what is the mean. Is there a way to adjust the STDV for each datum without keeping all of the previous values? This is needed basicaly for performance, so I won't need to read twice the same data (spend processing time) nor save the previous values (spend memory). Andrei Volodin and Penny Nom lui répond.
	Variance		2002-10-29
		Ade pose la question : I am trying to solve a standard deviation question, I have 30 data points to use, should I group the data before solving for variance or should I just use the raw data. Andrei Volodin lui répond.
	Range of values for standard deviation		2002-03-22
		Susan pose la question : What is the range of values for standard deviation? Is it between 0 and +3? Is it between +1 and +3? Andrei Volodin lui répond.
	Can the standard deviation ever = 0?		2002-02-16
		Karen pose la question : If given a class of 30 people who take a test with a mean of 80. Can the standard deviation ever = 0? If so, why? Penny Nom lui répond.
	Sample variance		2000-04-16
		Jonathan Freeman pose la question : I was just reading your article entitled "A Note on Standard Deviation" I'm now teaching a unit on s.d. and my students were wondering why one uses a denominator of n for a population and n-1 for a sample. I saw in your article that this is because "[the quantity] tends to underestimate sigma... and other technical reasons." To which my students again asked... "Why?" Could you please elaborate a bit on the "other technical reasons" perhaps in terms a high school senior (or their teacher...) could understand? Harley Weston lui répond.
	Standard Deviation		1999-07-11
		Anthony Fama pose la question : I have seen several answers to this question: If one standard deviation represents 68% of the population, what does two, three, four and five sigma [std deviation] represent? As stated, I have seen several different answers and thus, the impetus for my question. Harley Weston lui répond.
	Mean and Standard Deviation		1998-04-22
		Kit pose la question : i have a problem of maths. i think the level of the question is secondary. question: Find the mean and the standard deviation of the numbers:1, 3, 4, 5, 7. i hope u solve this question. thank you so much! Harley Weston lui répond.
	What is the variance of the difference of two binomials?		1996-02-08
		Chris Johnson pose la question : My co-workers and I have come up with different estimates of the z-statistic, and are in particular disagreement over the calculation of Variance for this problem. I am trying to find out, with a five percent level of significance, whether the new form yields a higher rate of return than the old form. Any thoughts, comments, or solutions? Harley Weston lui répond.

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