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Topic Sample Size Estimation

Sample Size Estimation

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This topic contains 15 replies, has 6 voices, and was last updated by  Robert Butler 2 weeks ago.

Viewing 16 posts - 1 through 16 (of 16 total)
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  • #206477 Reply

    Product validation group is facing a challenge in arriving at the right samples & right size of samples for test cases for certification. I need to build a sampling model which could determine the samples & samples size needed to release a product/patch to customers.
    We have identified the factors that could impact the sample size. I am not getting the way how to start with. Which approach should I prefer.
    Requesting the expert advice. Thanks in advance.

    #206539 Reply

    Prabhu V
    Participant
    Reputation - 1574
    Rank - Silver

    Hello Mr. Jain,

    Sampling technique needs what kind of data (continuous/discrete) you are going to handle at first.

    Kindly elaborate your query.

    Thanks and regards

    Prabhu V.

    #206587 Reply

    Abhishek
    Reputation - 33
    Rank - Aluminum

    Thanks Prabhu for the response.

    The 2 factors identified are continuous, rest 4 factors are discrete and the response is binary i.e. Pass/Fail.

    #206639 Reply

    Prabhu V
    Participant
    Reputation - 1574
    Rank - Silver

    Hello Mr. Jain,

    Kindly find the below formulas for calculating sample size based on your inputs.
    For continuous data

    N= (Z*S/E)^2

    N – Sample size
    Z – Constant for confidence level (like 1.645 – 90%, 1.96 – 95%, 2.575 – 99%)
    S – Standard deviation
    E – Precision or Error
    (Precision or Error is basically difference between target and actual parameter like mean, yield etc)
    Estimated Mean – True Mean (like X bar – µ)
    Estimated Yield – True Yield

    For discrete data

    N=(Z/E)^2*p(1-p)

    E – Precision or Error – level of precision desired from the sample in units of proportion
    p- Proportion

    Please feel free to post your queries in case if you want for clarifications.

    (Note: The above formulas are generic in nature, kindly support your sitaution for better clarity)

    Thanks and regards

    Prabhu V.

    #206739 Reply

    Baskar

    Hi Prabu

    Thanks for posting the formula for estimating sample. Can you plesae explain the below formula for discrete data with example. In my case we perform 89000 transaction per month. With this data how do we measure the sample size.

    N=(Z/E)^2*p(1-p)

    #206775 Reply

    Prabhu V
    Participant
    Reputation - 1574
    Rank - Silver

    Hello Baskar,

    Kindly find the below guidelines based on your reply.

    As you have not mentioned about your objective of sampling and its proportion, I am assuming your sampling objective is finding erroneous transactions in Population (89000 transactions) and erroneous proportion in Population is unknown currently (Assuming that you have 5% of transactions are erroneous).

    Erroneous: 5% of transactions (p = 0.05)

    Confidence level: 95% (Z = 1.96)

    Sampling Precision or Error: 3% (E = 0.03)

    N= (1.96/0.03)^2*(0.05(1-0.05)

    N= (1.96/0.03)^2*(0.05*0.95)

    N ~ 203 transactions

    Please feel free to post your quires/clarifications if in needed on above.

    Thanks and regards

    Prabhu V.

    #206779 Reply

    Baskar

    Thanks Prabu, for swift reply. The allowable error limit is 3% (SLA). Hence the p=0.03 right? then
    N=(1.96/0.03)^2*(0.03*(1-0.03))
    N=124
    My basic question? 124 sampling is for day or month? if it is for month then why we do perform very low sampling when we process 89k transactions.

    Thanks for your support

    #206783 Reply

    @abhi_jain80 : I’m going to challenge your decision to have a pass/fail response variable. You are probably measuring something that is on a continuous scale and making a determination that it has passed or failed. If so, then you will be better off using that continuous scale rather than the discrete. This will allow you later to find the relationship of the inputs to the output which will then provide you the ability to improve the output value. Using a pass/fail gives you very limited ability to do this.

    #206887 Reply

    Prabhu V
    Participant
    Reputation - 1574
    Rank - Silver

    Hello Baskar,

    On Addressing your query, I would like provide the following details

    1) The above sample size guideline is not with respect to the Population, rather with respect to the Population proportion (This formula is for calculating the statistically significant discrete data sample size).

    2) And also the above guideline did not guide you on the frequency or duration of samples from the Population.

    3) While considering the sample frequency/duration you can consider on some other factors like current erroneous transactions, resource availability for collecting the samples, etc.

    Please feel free to post your queries in case if you want any clarifications.

    Thanks and regards

    Prabhu V.

    #207227 Reply

    Baskar

    Thanks Prabhu, it make sense.

    Prabhu will you be able to assist me with different topic on “BENCH MARKING”. I have few clarification to verify with you

    #207237 Reply

    Prabhu V
    Participant
    Reputation - 1574
    Rank - Silver

    Hello Baskar,

    Thanks for your feedback.

    You can very well post your query on any LSS (Lean & Six sigma) topics in this forum.

    Definitely, it will be answered by someone who is having sufficient knowledge and expertise (of course if some suitable stuff with me means, surely will reply to your query)

    If you want to contact me directly you can contact @ prabhu_vspj@yahoo.com or through LinkedIn

    All the best!!!

    Regards
    Prabhu V.

    #207279 Reply

    Hi Prabhu,
    I am from software industry & any software release has to go through test certification. Testing team basis on samples certify the release.
    I need to develop the sampling model which could help them in identifying the right sampling size as well as right samples.
    What should be my approach?? Appreciate your response.
    Regards,
    Abhi

    #207291 Reply

    Prabhu V
    Participant
    Reputation - 1574
    Rank - Silver

    Hello Abhi,

    As already mentioned that the sampling techniques will be decided based on the data type you’re going to handle.

    Hence if you can able to provide more details means, it will be useful to clarify your query.

    For example as Mr. Baskar has explained about his situation.

    Thanks and regards

    Prabhu V.

    #677801 Reply

    Kofi Delove

    Please can you help me to use a formula to calculate a sample size from a population of 1,534 and explain to me vividly how you arrived at the answer. Thanks.

    #677804 Reply

    Kofi – The more details you provide, the more likely you are to get a response. What do YOU think you should do? Why or why not? The iSixSigma audience is helpful, but they like to see that someone is putting forth a good-faith effort; they are not here to do your homework for you.

    #677805 Reply

    As posed, your question has no answer other than to say that the minimum sample size could be 1 and the maximum sample size could be 1534. To provide anything meaningful to you it will be necessary for you to give us a detailed description of what it is that you are trying to do.

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