can someone tell me about the difference between coefficient of variance and Z-score. What do we calculate ( i mean either Z-value OR Coefficient of variance) in order to analyze the data

thanks:

can someone tell me about the difference between coefficient of variance and Z-score. What do we calculate ( i mean either Z-value OR Coefficient of variance) in order to analyze the data
thanks:

Hi,

The z score or z value is simply the number of standard deviations a value is from the mean, assuming a normal distribution. For example, you could calculate how many standard deviations (z value) a specification limit is from the mean.

The coefficient of variation is the standard deviation divided by the mean.

http://www.itl.nist.gov/div898/handbook/eda/section3/eda3661.htm

Either or both values can be used to analyze data. I also recommend plotting the data so you can view it graphically. This will help detect anomalies.

Wes R.

If I have plenty of data to be analyzed, what is the best indicator of variance, Z-value or coeficient of variance?
thanks

What information are you trying to obtain? If you have a lot of data, the best representation of how that data varies from the mean is the variance, or the square root, which is the standard deviation.

Z value is a representation used for calculating area under the curve (typically). Say you have a bunch of data with a mean and standard deviation. Assume normality on the data. If you were interested in what percentage of your data was above/below a certain value, that is where you would use a Z value.

That is the Texas version. There are some brilliant people here who can provide a much better definition.

But, I am interested in what you are trying to ascertain from the data.

If I have plenty of data to be analyzed, what is the best indicator of variance, Z-value or coeficient of variance?
thanks

The coefficient of variation is more often used when comparing variation of processes that have substantially different means. For example, liquid soap for washing clothes is available in many different size containers. You could compare the different containers by taking the standard deviation for each and dividing by the mean for that size container.

Wes R.