standard deviation

Hi, quite a basic question here but I can't find a solid answer. If I had a data set of 10 points, and I chose to add 4 new data points to it for example, can I use the same original standard deviation? Or must I re-calculate it? Is it possible to add the new data points with a specific number...

Hi Im kinda new to statistics and would very much appreciate some help. I have finally understood the standard deviation formula and the reason behind every step/calculation. But..lets talk about stock market. a) why does the stock market write s.dev in percentage? I had the impression that...

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Hi, I'm wondering if we could apply standard deviation or IQR on our daily log on time? I have a dataset with many machine ID that has many log in records for entire month. I have removed the weekend data and left with log in data of over 1000 machines. From the dataset, each machines has...

Hi! I am involved in the writing of a thesis, where two raters are running a test-retest study to test the intra- and inter-rater reliability of a clinical test. Here the Standard Error of Measurement (SEM) needs to be reported, and the following formula should be used: SEM=SD x √(1-ICC). I...

Why is it ok to estimate the population variance with the sample variance formula (i.e. the unbiased estimate of the variance). I understand how we can build a confidence interval using the central limit theorem and the following formula . But, the unbiased estimate of the variance means that...

Very dear geeks :cool:! I am new in this forum. I am a french post-doc in marine ecology and I am especially interested in trophic relationships. I am currently analyzing time series. I have to admit that time series are definitely one of my strongest Achilles heels, I am actually afraid of...

I want to estimate the accuracy and precision of aggregate data from an instrument that measures a variable that fluctuates over time by comparing a sample of its measurements to concurrent measurements made by a reference instrument. For this purpose, assume that the reference instrument...

Hi guys!. I need some statistics help here. I have three producttypes; Plates, spoons and mugs This is what i know Spoons: Mean = 565,87 Variance = 50677,28 Standard Deviation = 225,12 Correlation with plates= 0,8394 Correlation with mugs = 0,8271 Plates: Mean = 1806,83 Variance...

Hello, I want to back-calculate the minimum sample size for a mechanical experiment. I have a known mean and standard deviation of a statistical population. From the statistical population I chose two samples with means and standard variances I could estimate. My question is: How can I...

Hey everyone, I was hoping someone could help me. Im applying for a job, and am trying to work out my overall ranking in two seperate exams so that I can include this in the application. Could someone please tell me if my calculation is correct? I have attached the file with my calculation...

I have 3 specimens (A, B & C) and 5 sets of observations from A & B but only 4 from C. Each observation has been reported as a mean & a standard deviation. I do not have access to the underlying data. I am curious about whether the samples are statistically different from each other as far as...

Hey guys, This is my first thread on this forum so please bare with me as I try to be as concise as possible, I'll then write down my questions at the end of the thread. I'm working on some class notes, and stumbled upon this problem that confuses me on some point: "The drying time of a...

Is there a way to calculate the Normal Distribution of a set of multiple Standard Deviations (SD) and Means (µ)? I am afraid I do no have Access to the raw data from which the SD´s and µ´s were calculated. Many thanks in advance

Hi All, I would like to inquire how to decide whether Dataset A or Dataset B would be reliable based on their coefficient of variation, number of data points and mean value. What kind of factors could be considered? I am not searching for the direct answer but rather to jump into the...

Hi, I use Excel to analyze data. On one of my workbooks, I have about 30,000 rows of intraday data. Sometimes I might have 0 datapoints on a particular day, some days I might have 15 datapoints, and other days 20 datapoints. On average, I have about, 5,500 datapoints over the period of a...

Hi All, I am measuring the height of a tank over time to calculate the flux. -F is the volume of tank F -On every time point, the volume is measured 3 times (since the way of measuring is quite fault sensitive) So F has an average and a standard deviation. -Flux: (F(t)−F(t−1))/dt, in which dt...

I just came to the sad conclusion that I have not been maintaining my statistical skills enough the last years, and therefore I must kindly ask for help in this easy question: How to find standard deviations from variable A for individuals in a group adjusted for effect of variable B? I have a...

Hi :) I am new here on the forum and find it a bit difficult to learn the way to go at different statistics/probability - problems. For the most times I am able to figure it out myself doing some research, but the last two problems has got me stuck for a few days. I would be really thankful for...

Theoretical question: So say there is a course where if you score two standard deviations below the mean, you will fail the course. The class average will be roughly a 75%, not sure what to set as the baseline for standard dev, and say 150 people are in the class. One person is added to the...