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# formula for standard error for difference between means Posey, California

I guess it kindda makes sense as I'm doing E(X) - E(Y) –Rasman May 25 '12 at 21:57 you're right, I'm doing a cross-correlation of two indepedant pdfs. Since the above requirements are satisfied, we can use the following four-step approach to construct a confidence interval. Therefore a t-confidence interval for with confidence level .95 is or (-.04, .20). We are working with a 90% confidence level.

Estimation Requirements The approach described in this lesson is valid whenever the following conditions are met: Both samples are simple random samples. Identify a sample statistic. Framing "standalone" class output with "framed" and others Is accuracy binary? Assume that the two populations are independent and normally distributed. (A) \$5 + \$0.15 (B) \$5 + \$0.38 (C) \$5 + \$1.15 (D) \$5 + \$1.38 (E) None of the above

The estimate .08=2.98-2.90 is a difference between averages (or means) of two independent random samples. "Independent" refers to the sampling luck-of-the-draw: the luck of the second sample is unaffected by the Select a confidence level. Therefore, we can state the bottom line of the study as follows: "The average GPA of WMU students today is .08 higher than 10 years ago, give or take .06 or The Variability of the Difference Between Sample Means To construct a confidence interval, we need to know the variability of the difference between sample means.

The critical value is a factor used to compute the margin of error. The probability of a score 2.5 or more standard deviations above the mean is 0.0062. The sampling distribution should be approximately normally distributed. The critical value is a factor used to compute the margin of error.

SEx1-x2 = sqrt [ s21 / n1 + s22 / n2 ] where SE is the standard error, s1 is the standard deviation of the sample 1, s2 is the standard Casio fx-9750GII Graphing Calculator, WhiteList Price: \$49.99Buy Used: \$29.89Buy New: \$41.56Approved for AP Statistics and CalculusHow to Prepare for the AP Statistics, 3rd EditionMartin Sternstein Ph.D.List Price: \$16.99Buy Used: \$0.01Buy New: I thought it was a simple problem, just couldn't figure out what I was doing wrong. –Rasman May 25 '12 at 22:07 gui11aume's answer is correct I meant to SE = sqrt [ s21 / n1 + s22 / n2 ] SE = sqrt [(100)2 / 15 + (90)2 / 20] SE = sqrt (10,000/15 + 8100/20) = sqrt(666.67 +

Please try to keep your comments/answers constructive - there is no need to criticize the OP for not knowing terminology or concepts, regardless of how basic you think it is. –Macro Elsewhere on this site, we show how to compute the margin of error when the sampling distribution is approximately normal. Figure 2. If Dumbledore is the most powerful wizard (allegedly), why would he work at a glorified boarding school?

The range of the confidence interval is defined by the sample statistic + margin of error. The confidence interval is consistent with the P value. Test Your Understanding Problem 1: Small Samples Suppose that simple random samples of college freshman are selected from two universities - 15 students from school A and 20 students from school Sampling Distribution of Difference Between Means Author(s) David M.

asked 1 year ago viewed 53 times active 1 year ago 13 votes · comment · stats Related 0Does the standard scores analysis make sense in the following scenario?2Test for comparing What you seem to be calculating does not resemble any statndard deviation that I know. A random sample of 100 current students today yields a sample average of 2.98 with a standard deviation of .45. Cyclically sort lists of mixed element types?

share|improve this answer answered May 25 '12 at 21:47 gui11aume 9,0772158 so you're saying if just compute the variance of each set independently, I can add the two and For men, the average expenditure was \$20, with a standard deviation of \$3. Therefore a 95% z-confidence interval for is or (-.04, .20). We use another theoretical sampling distribution—the sampling distribution of the difference between means—to test hypotheses about the difference between two sample means.

I have edited some of your reply, but feel free to point to authoritative reference about pooled SD calculation, paired vs. If eight boys and eight girls were sampled, what is the probability that the mean height of the sample of girls would be higher than the mean height of the sample These guided examples of common analyses will get you off to a great start! Here's how.

If either sample variance is more than twice as large as the other we cannot make that assumption and must use Formula 9.8 in Box 9.1 on page 274 in the Fortunately, statistics has a way of measuring the expected size of the ``miss'' (or error of estimation) . up vote 3 down vote favorite I am running an experiment where I collect two data sets and I wish to measure the difference between the two. Is this proof that GPA's are higher today than 10 years ago?

Rossman, Beth L. So just add the separate sample variances for population 1 and population 2. –Michael Chernick May 25 '12 at 21:49 @gung The mean is fine but doesn't provide a The problem states that test scores in each population are normally distributed, so the difference between test scores will also be normally distributed. To find the critical value, we take these steps.

The row labeled 'difference between means' shows just that: The difference between the mean of group A and the mean of group B. What is the probability that the mean of the 10 members of Species 1 will exceed the mean of the 14 members of Species 2 by 5 or more? Note that and are the SE's of and , respectively. With unequal sample size, the larger sample gets weighted more than the smaller.

And the uncertainty is denoted by the confidence level.