Linked Questions

0 votes
1 answer
1k views

T-test or Mann-Whitney U test [duplicate]

Given the central limit theorem, can you always use a t-test to test a difference between two groups even if the data are not normally distributed but the sample size is large enough? Stated in ...
user avatar
  • 13
1 vote
1 answer
64 views

Is it safe to use one sample-t test with a dataset of size 5000 while the population distribution is not normal? [duplicate]

I have a random variable X, number of hours that kids from 10-12 years old spend on video games in one month in a specific country, and I want to test the hypothesis that the mean of my population $...
user avatar
47 votes
5 answers
102k views

What references should be cited to support using 30 as a large enough sample size?

I have read/heard many times that the sample size of at least 30 units is considered as "large sample" (normality assumptions of means usually approximately holds due to the CLT, ...). Therefore, in ...
user avatar
  • 1,251
15 votes
2 answers
7k views

Independent samples t-test: Do data really need to be normally distributed for large sample sizes?

Let's say I want to test if two independent samples have different means. I know the underlying distribution is not normal. If I understand correctly, my test statistic is the mean, and for large ...
user avatar
  • 547
12 votes
1 answer
3k views

Is bootstrapping appropriate for this continuous data?

I'm a complete newbie :) I'm doing a study with a sample size of 10,000 from a population of about 745,000. Each sample represents a "percentage similarity". The great majority of the samples are ...
user avatar
3 votes
3 answers
12k views

Repeated measures ANOVA or Friedman test?

I have a study with 35 subjects who received hypercoagulability testing at 4 different times (before surgery, after, at 1 week, and at 1 month). Each subject has 9 different test of hyper ...
user avatar
6 votes
2 answers
2k views

Can we ALWAYS assume normal distribution if n >30?

I'm in a debate with a coworker and I'm starting to wonder if I'm wrong but the internet is confusing me more. We have continuous data $[0, \infty)$ that is retrospectively selected on individuals. ...
user avatar
  • 175
3 votes
1 answer
3k views

Is having too high variance a problem when doing t-test

I am comparing scores of two student groups using t-test (in scikit-learn). Each group has different number of students. Since there are considerable numbers of 0 scores in my data, the standard ...
user avatar
  • 825
3 votes
3 answers
1k views

If the parent distribution is skewed, but the sample size is greater than 30, is the distribution of the sample mean nearly Normal?

I have my AP Stats exam tomorrow and had this question. I apologize if it is too simplistic for this forum. I'm pretty sure the sample's distribution is nearly normal, but not 100%, can someone ...
user avatar
  • 35
2 votes
2 answers
4k views

Do statistical tests require a normal distribution in the sample or in the population?

Certaint tests, such as the t-test, require a normal distribution. Yet I have never quite understood what exactly has to be normally distributed. Let's use age as an example. Age is rarely normally ...
user avatar
1 vote
0 answers
3k views

R: Shapiro-Wilk test for log-normal distribution

I would like to use a t-test for hypothesis testing on the amount of calories consumed by women per day. The distribution of this variable is right-skewed and a log-transformation increase its ...
user avatar
5 votes
2 answers
220 views

Related to exponential distribution

I am a beginner in statistics.(and probability theory too).I studied Exponential distribution and just started doing problems when I got stuck in the following one: Suppose that $X_1, . . . , X_n$ ...
user avatar
  • 1,047
1 vote
1 answer
1k views

Big sample size (n>50.000), but still highly skewed. Is central limit theorem still valid?

I have 12 samples with approx. 50.000 data points each. I got it from a content analysis of Reddit comments. The data is generated by analyzing the comments with LIWC tool and it gives me information ...
user avatar
2 votes
1 answer
1k views

Statistic on non-normalized data

Not that strong in statistics, so I need a little help getting started with some data I've gathered. In my experiment subjects had to perform tasks while I took time for them to complete it. Now, I ...
user avatar
0 votes
1 answer
546 views

Are 25 sample means, each of size 5, approximately normally distributed?

If I draw five simple random sample observations from a non-normal population, calculate their mean, and repeat 24 more times, will the 25 means I've computed approximate a normal distribution? The ...
user avatar

15 30 50 per page