How to calculate Sample Size
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- Опубликовано: 4 фев 2009
- A video on how to calculate the sample size. Includes discussion on how the standard deviation impacts sample size too.
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My left ear really likes this video
Damn i thought my headphones broke
@@jephonecanas3148 same, I almost got so worried
@@jephonecanas3148 me too
Hahahahahhaha
You Rawk! Test on Monday and this is helping so much! Thanks for making Stats easy to follow!
Yes you are correct. Either equation should give you the sample size. Do make sure you watch the video on sample size for proportions (see link in video description).
Short, sweet and straight to the point. thank you. So easy to follow.
Questions are always good. SD is the standard deviation and it tells how disperse the data. If you have a high SD you will have a bigger samples size.
E or error is the acceptable error. It is usually given or the researcher decides on it.
Good luck in your classes.
Good luck on your test, you can do it!
If you are looking at populations that are not normally distributing you should think of ways you could segment the data so it more closely fit a normal distribution. For example, if I was looking at heights of all adults versus heights of adult females and heights of adult males.
That would actually be equation for sample size for proportions. I added a link in the video description to a video that discusses using this formula.
Make sure you like MyBookSucks on FaceBook (see link in video description). This will help other students find the educational videos.
You make statistics fun!
Your voice sounds like Russel from ownage pranks. Besides that, very helpful video.
Hi. How can I explain results statistically significant but not reached the magnitude (delta) pre established at the sample size calculation?
Many thanks for your videos! They are really informative.
Can I just check my understanding on one point. Is the error rate different from the margin of error?
jon robinson Jon it really depends on the context. I have not heard (or used error rate) synonymous with margin or error. I would suggest you ask this same question to your professor.
Prof i am probably naive asking this.
You have a population of say 100 cases and worked out standard deviation, standard error and finally the sample size which worked to be say 75.
Would you select 75 or 100 cases from your population for your study?
If you chose only 75, would you be selective or randomly chose the 75?
Also, can we use the same method for discrete data as well.....
very very nice video. thank you
I am not sure what is "RCT" or perhaps it does not matter. The sample size does not depend on the type of study, but the number of dropouts that are excluded would impact the sample size. From what you have told me I would say 1 is false.
under which conditions should i use prevalence sample size calculation?
When power analysis to be used to identify the sample size? Why it is not discussed in the above video?
Could you please help to understand as to how calculate Error Rate which you used in above video...
Thantk you for the Video, what is the usually used case number "n=30" in biomedical field comes from? there is hardly reference on the statistical textbook and internet sources, thank you very much.
Great video. Let's say you don't know the standard deviation in a population....how do you determine what sample size will be adequate?
same question here
hey jeff did you figure out the answer to that
I have seen a few other equations for this using confidence intervals and standard error but some knowledge of the STDEV is always needed. it really is the deciding factor.
You can use a standard deviation from a previous pilot sample.
You need to run something called pilot experiment before the main experiment
Easy to understand. Thanks. But what happen with different confidence lever.?
this is standard deviation of what? If I need to find buying behaviour of people of a city with respect to daily internet usage frequency..which factor's standard deviation should i look at?
My right ear enjoyed this knowledge
Sounds like you are frustrated, but don't be hate'n! I post a lot of videos which are available for free.
Morning Sir
1.96 is for Gaussian or distribs that approach Gaussian. What if we are out of this domain? What if we have a Pareto distrib ?
What if the population you are going to take the sample is not represented by normal distribution. Would this formula be still valid for calculating sample size?
Thank you Sir
Who's formula are you using ?
And is E always 4 ?
I have a weird problem in fitting negative binomial where the mean and variance is given and I have calculated the P(X=x). But cannot determine E=N. P(X=x), because N is not given.
thank you
Wow! Thanks for coming to my defense. Make sure you like MyBookSucks on FaceBook (see video description). If you send me your address on FB, then I will send you a MyBookSucks t-shirt too.
I wanna know that the formula does not change if it requires the minimum of sample size?
How do we calculate a standard deviation before we start our thesis
This is done by running a pilot experiment before the main experiment starts.
is there any standard error rate or it is a user-defined.please reply me
The calculation of sample size in order to...decide on sample size, is kinda chicken and egg. You first need means and SD, which means you needed to conduct the experiment already. So what's the point? It only helps on the next experiment.
Yeah I'm actually thinking about that
Why did you choose 4 as the error? How do we estimate this error properly?
This video was helpful. Thank You!
How should we calculate sample size for a pilot study in preparation for an RCT
Pooja Dewan
can you please give a reference for that formula and method
How do I find the error rate?
from previous studies.. you have read the articles.. it is going to give you an idea..
Error Rate = x-true average
True Average is that greek symbol called 'Mu'.
Sir..... just wanted to ask a question which had come in one of the examinations in my country.....
"Which of the options is false about RCT -
1) sample size depends on type of study
2) dropouts are excluded from the study
Sound only in one side....I thought it was silent because I only had one earphone in. Where do you get error rate? How does your lot size affect this?
This is short and interesting. Please what is the name and source of the formula
Thanks
How we can reference this formula?
in case you didn't notice that it's the END 😂
How do i find the sample size when they only give me phat = .3 and standardized test statistic z = -10? Aslo Ho: p=.35 and Ha: p
How did you take sd 20 or 25
but how do you get your error rate?
How do you decide error rate?
How can we calculate standard deviation before starting the study? thank u
True sigma is rarely known. In such a case, you must make an educated guess. If you can find pre-existing data on your population of interest or a another population that is likely similar, you can use that to estimate sigma.
Prof How do i get the standard deviation?
and where is the standard deviation from??
is the error rate same as the margin of error?
HOW TO GET STANDARD DEVIATION TO CALCULATE SAMPLE SIZE, IS IT FROM PREVIOUS STUDIES??? OR FROM SAME STUDY WHICH HE IS GOING FOR MAIN STUDY???
can someone explain to me the graph please
If we don't know the population standard deviation only population number we know and minimum sample erro with high coincidence...then which formula
why is my formula different? mines is n=Z^2[p(11-p)]/D^2
any reference for this formula please?
How error rate of 4 was decided ??
How do I get sample size for a population estimate..
What is the name of the formula?
someone kindly help to calculate sample size, prevalance 91%.
DIVIDED BY the error rate squared, not TIMES the error rate squared.
How error rate of 4 was decided ?? 4%? what is the unit?
the SD is for what??? and how you calculate the E....it is like solving a silly mathematical equation no more.....but any way, thank you
Is there a name for this formula?
Take a deep breath and count to 5
How to calculate the E???
Where did the 3.84 come from? You didin't explained! Thanks!
How was E calculated ??
you have not indicated how the standard deviation and the error component are calculated from the population
if you don't know what the point estimate is, don't watch this video, first go and watch one about the point estimate! and MAYBE then you will be able to understand this one! and if NOT then "get over yourself" because you will not get it ever..O_o
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For real situation, we never know how much is population.
We shouldnt use this equation unless we can control the population.
why is my left ear getting caressed?
Not very useful as I have the same question everyone has.
Could you please help to understand as to how calculate Error Rate which you used in above video...
+Ashok Lodhi The error rate or accepted margin of error is what you determine. Typically, it is plus or minus 2.5%
+statisticsfun Thanks for taking out time and replying on my query. I also wanted to know that how do we do sampling for Discrete Data. Many thanks for your help and valuable free videos...
+statisticsfun Sorry I still don't understand how to determine the error rate.. It is 2.5% of what?