Why is 30 the usual amount of participants for a study?
407793
Because 30 is the magical number statisticians decided upon to indicate whether a population can be assumed to have a normal distribution.\n\nEdit:\nMore on standard normal distributions and why they are so important to statistical analysis here: http://en.wikipedia.org/wiki/Standard_normal_table\n\nIdeally you want as many participants in a study as you can manage but costs often get in the way making 30 a popular number.\n\nRegards,\nArmus
579180
if you're talking about in statistics, a convenience sample would be asking the first 100 people who walk past you on the street the same question. it tends to create biased results.
73353
Statistics can be realied upon to a certain degree, but it really depends on where the stats are coming from, are they coming from a realiable source, or from a friend of a friend of a friend?\nMost statistics are made up from a small survey of people, for example viewers who watched a particular show. The actual number of people that watched the show may be 20,000, but these are only the people who have the equiptment attached to their tv set to show what they watched and when so to get a realistic figure they may count each person as 1,000 to get a more realistic figure. In actual fact everyone else may have been watching something else.
1152126
it is unclear what you mean when you say that a population is increasing from 0 to 30. is it a finite poulation? do the items in the population take values from 1 to 30? As you have asked it, this question is impossible to answer.
971624
about 30 fluently, mostly from the last Juz.\n\nwish I could learn more.  *sigh*
246807
I can't count, so don't blame me if I get this wrong.\nLet n be the number of participants.\nSince it's a close circuit, the people in front of him are in a sense also behind him so there ara (n-1) people both ahead and behind him.\nso (1/5+5/6)(n-1)=n\n31/30*n -31/30=n\n1/30*n=31/30\nthus n=31\n31 total people
192874
about 300,000,000 give or take
1009792
Assuming it started 4 weeks before World Cup even began, and an average of 25 times the question is asked per day ... \nSo it's uhm .. not that many actually ... just a few hundred times!!! LOL ...
553936
An average is between 20% - 30%...
753276
You need to specify a probability distribution for the number of incoming students. That would most likely be modeled by a Poisson distributed random variable (as quite often in Queuing Theory) with rate lambda>0. I will denote it by X and the number of teachers by n..\n\nThen the criterion for the number of teachers reads as follows:\n\nP(X>n*2.5)<=0.1\n1-P(X<=n*2.5)<=0.9\nP(X<=n*2.5)>=0.1.\nF(n*2.5)>=0.1.\n\n(where F is the cdf of the Poisson distribution)\n\nYou can solve it for n, or, for large n, you can also use a normal approximation by using the central limit theorem. Tell me if you're interested how this is done by using "Add details".
808395
You can't apply statistics (to anything) unless you have a sufficient number of values to work with.  For example, if you took a poll of who people were going to vote for, if you only asked 5 people, you might not get an accurate representation - but if you ask 5000 then the margin of error gets smaller.  With molecules, there are millions of them.
979806
Are you asking for sheer number or percentage of a group?  Your question is unclear.
118042
randomization is a myth, try doing something randomly and you have picked a path. observation is just that you would not have input to the study.
795974
the sample would be ....for example: if you used a group of 30 women between that ranged from18-22yrs...the sample mean would be women of the age 20.
58455
Probably about 40 but half of them don't know it yet :)
765612
Each cycle appears to be a week long, so I guess what is happening is that more people use LinkedIn on some days of the week than others (perhaps it gets a lot of usage on weekends and not so much on weekdays...or something like that).
381147
30,000 students - look at the brochure below