# Number of measurements

#### altf2

##### New Member
Dear mates, I have to solve this problem and is breaking my head, I simply can't figure out how:

What is the minimum number of measurements I need to know in order to have the average value (of that measurements) being representative and reliable

I'll appreciate any help

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#### obh

##### Member
The answer depends on the standard deviation of the population. You need to calculate the confidence interval.

#### altf2

##### New Member
The answer depends on the standard deviation of the population. You need to calculate the confidence interval.
thanks for the answer but that seems to be for the sample size and I'm looking for the number of measurements

#### GretaGarbo

##### Human
thanks for the answer but that seems to be for the sample size and I'm looking for the number of measurements
Hmm, usually the sample size is equal to the number or measurements. What do you (altf2) mean by this?

Also, one way a sample can be "representative" is when every individual has the same chance of being included, like in simple random sampling.

#### hlsmith

##### Not a robit
@altf2

Yes, please define your units / subjects so you do not break our brains as well. Do you mean how many times do I need to consistently weigh myself to get my average weight, or do you have a sample, or do you have a sample with repeated measures at the unit level?