Found a good clue why sample size 30 would be enough. It all rely on Central limit theorem
- The distribution of an average tends to be
Thus, the Central Limit theorem is the foundation for many statistical procedures, including Quality Control Charts, because the distribution of the phenomenon under study does not have to be
When the sample size approaches 30, we don't have to worry about the distribution of the population since it can be safely assumed to be normal for inference purposes.
Still don't belive, click here.
2 comments:
thank you thank you thank you for pointing out the theorem. For the last few years when people refer to me as 'expert' or 'Dr.' (mistaken from the last name Do hahahah) I have to talk and act and nod like a real one [expert/dr.], and one thing i've always been la(n ta(n about is the 30 sample.
Conclusion:
1) market study is only for suckers to make market research companies rich. Just decide whatever you want in marketing, because at the end of the day there would be some of the average suck up to your idea/product anyway. Just make sure the population (sample) is big enough.
2) I always try to find a shortcut for everythings that I have to find an answer. For this 'sample of 30' I choose to not take short cut by read books and study hard to find out why, then gave up after wasting many many months. Then random check for new pictures of Moc then found the answer. Lesson learn: one random short cut worth 10 months study.
Market research is like going to fortune teller. You pay them to say good things. So they will say what you want to hear.
And it wasn't too bad. It give you confident to go big, because you know God is there to radomly back up your ass
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