# standard deviation

1. ### Citation needed for removing 3 Stdev outliers

Hi, In a research paper, I had remove values that were 3 standard deviations away from the mean. The values simply didn't make any sense. I have been searching all over for a citation supporting the 3 standard deviation rule but haven't found much as most researchers don't seem to include...
2. ### Standard deviation - how many samples to I need to measure to get a "good" one?

I was looking at Minitab 16's Power and Sample Size calculation tool for a one sample t-test. If you're not familiar with it, you can put in 2 of the 3 factors: sample size, differences, and power values. You also have to put in the standard deviation. This got me thinking. How do you know...
3. ### Standard deviation as a percentage

Hi i'm new here and have a really quick question, How do you interpret a standard deviation given as a percentage (in this case 20%)? I need to use the variance in further calculations (working out type i and ii errors), the data is normally distributed, and the sample size is 30, i have...
4. ### Uncertainty in Standard Deviation

The 95% confidence intervals for the standard deviation (SD) of 5 measurements is approximately 0.6*SD to 2.87*SD. The measurements are laser analyses to determine the atomic composition of a solid material. If each of the 5 measurements, stated above, actually consist of the average of 50...
5. ### Calculating 95% confidence interval from mean, SD and number of subjects

Dear All I have been asked to present some information from a series of published articles according to Mean (+/- 95% Confidence Interval). The statistical summaries are generally presented as: Number of subjects (n) Mean (X) Standard deviation of the mean (sd) How do I calculate the...
6. ### reliable results?

Hi, my name is Dave. I am a recent graduate trying to pass a licensing-exam with the state of California. I think I passed the test (my score=73%), but they use a criterion-referencing method where results are compared to a criterion (their passing score= 75%) rather than to the mean. The idea...
7. ### Random Variable X

So this question is on my practice final, and the professor provided the work for how to solve it and I cannot figure it out. Suppose that the random variable X has a mean u = 5 and standard deviation o=8. The mean and standard deviation of Y=2X-4 is? The answer is 6 and 16, respectfully...
8. ### help for task in R programming language

This is my task. I don't know how to solve it in R studio. Please help me!!! Simulate: a) 15 values from N(0,1) distribution b) 50 values from N(1,5) distribution c) 30 values from exp distribution with parametar 2 For all these I hade to find mean, standard deviation, deviation. And...
9. ### Probability without z-score?

Estimate mean of male students on campus. Standard deviation of the heights of young men is about 2.8 inches. Suppose (unknown to you) the mean height of all male students is 70 inches. a) If you choose one student at random, what is the probability that he is between 69 and 71 inches tall...
10. ### Finding IRQ from standard deviation and normal distribution

Here's my problem. Any help or insight would be greatly appreciated: A report provided a standard deviation on waiting time to single room occupancy hotels to be 12.9 days. Given that the waiting times follow a Normal distribution, what is the IQR here (single number)? Thanks in advance!!
11. ### Question Help ASAP!

The scores on a standardized English placement exam are normally distributed with a mean of 100 and a variance of 81. The top 10% of students will be placed in an Honours English class. What score must a student get on the placement test in order to be placed in Honours English? THANKS!!
12. ### Won't Repeated Measures GLM give estimated Standard Deviations ?

Hello, I am novice so I hope that my question formuling will be understandable.. I am using the RM GLM and wonder whether some option (I doubt) or a syntax command would let SPSS calculate my between subjects factors' estimated Standard Deviations, similarly to the Means and Standard...
13. ### statistics applied to flow

Hi there, I have been trying to solve the problem below, but have had difficulties in solving it. I would really appreciate it if anyone could explain to me how to solve it. The standard deviation of the flow is s=0.3 occuring where the mean concentration is 0.9. The mean concentration is...
14. ### Impulse Response Functions

I have obtained point estimates for impulse response functions. How can I tell if it's values are significant?
15. ### multiplying Standard error of means

Hi guys, I am new here (and also to statistics :o). I have a data set of many measurements. For each one of them I calculated the mean and the SD (deviation). From that I calculated separately for each of the data set a SEM. Now I would like to multiply, divide add and subtract this data...
16. ### Normal Distribution & possible Standard Deviation error

I have collected final sales data for over 12,000 sales of a single particular item. The prices range from $0.01 to a little over$4.00. I calculate a mean of $0.60. My problem is my standard deviation is$0.58. That doesn't make sense to me. If I move 2sd to the left I am at a negative number...
17. ### "averaging" standard deviations

Hello, I've been given the mean and standard deviation of many sets of the same measurement (bead size). So, I basically have a list of means and a list of corresponding standard deviations. I need to pool and analyze the data to figure out the overall distribution of bead size over these...
18. ### Difference between standard deviation and standard error

Hi, what exactly is the difference between the SD and SE? I read through the wikipedia article but dont really understand the difference. Can anyone help? Cheers beginner