All Questions
223 questions
7
votes
1
answer
320
views
Can you use the paired t-test in what seems like an unpaired t-test situation?
I came across a situation where a large retailer is testing a new retail program. It selected specific pilot retail stores to test this program. Next, it selected a control group of retail stores so ...
- 7,882
4
votes
1
answer
119
views
$p$-values from two-sample $t$-tests of resampled vector clump at $p > 0.7$
I have created a vector of length 400 with 6 unique values of relatively equal proportions (1-6). I have drawn two random samples from the vector, each $n=26$, 10,000 times, performed $t$-tests, added ...
- 41
3
votes
3
answers
6k
views
Can you do a paired t test in SPSS or GraphPad with only means, errors and N?
I have to verify some results. I have only the mean and its st. error, not the raw data. In a research paper they did a paired t test. Is it possible to check whether their p value is right by only ...
- 61
1
vote
1
answer
8k
views
How to calculate p-value for t-test if original data is not available? [duplicate]
I have two (normally distributed) samples:
First: n=50 mean=3 sd=2
Second: n=40 mean=3.5 sd=1.9
Is this enough to perform two-sample and two-sided Student's t-test with equal variances? If yes, how ...
- 3,979
6
votes
1
answer
478
views
Why so many large p-values when I repeat an experiment?
I have a quick question:
In using a t.test for multiple experiments, I got one p-value for each experiment.
When I plot the histogram of these p-values, I find the distribution looks like a bell-...
- 1,013
1
vote
1
answer
93
views
Strange behavior of location-tests for different datasets
I have two datasets, $D1$ and $D2$, each containing many samples $S_i$ of 100 numbers, each sample from a different (unknown) population. For example:
$S_1=\{0.125, 0.122, 0.053, \dots\} \\
S_2=\{0....
- 237
12
votes
1
answer
129k
views
"Accept null hypothesis" or "fail to reject the null hypothesis"? [duplicate]
I'm trying to conduct a Student's t-test for a table of values while trying to follow the explanation and details found on this website. I understand that if the p-value is
<.01 then it's really ...
- 223
4
votes
2
answers
514
views
Computing p-values
I am a computer engineer, living in a digital world. I have no probabilistic background besides a probability course in the University and tried to grasp the Fisher's idea and have got the following ...
- 583
0
votes
1
answer
5k
views
how to bootstrap p-value in ttest in Stata?
Suppose I need to run ttest bhar12=0 and the output comes as:
...
- 3
2
votes
1
answer
3k
views
Figuring out an effect size with a P value for a t-test, sample means, and sample sizes
An author did not report an effect size so I am hoping you might be able to help me calculate it.
I know the Means are:
Condition 1: 326
Condition 2: 558
Sample ...
- 1,220
5
votes
3
answers
30k
views
How should I interpret the p-values (i.e. t-tests) in regressions, and can I use them for feature selection?
I'm trying to do an OLS regression with several independent variables, and want to better understand how to interpret the p-values from doing the t-tests on the independent variables within my ...
- 779
8
votes
1
answer
12k
views
Is significance of the p-value reliable with extremely small sample sizes? [duplicate]
As I'm completely new to statistics and clinical trials, I would ask you for help and clarification.
Let's assume we have 2 really small samples (each of n = 2, or so) derived from two normally ...
- 83
2
votes
3
answers
142
views
Significant differences and related variables
I am reading a paper in which a statistical difference has been found between two treatment groups for a variable A (p=.05), but not for variables B (p=.06) and C(p=.06), even though A=B-C. Is this ...
- 21
60
votes
4
answers
156k
views
Manually Calculating P value from t-value in t-test
I have a sample dataset with 31 values. I ran a two-tailed t-test using R to test if the true mean is equal to 10:
t.test(x=data, mu=10, conf.level=0.95)
Output:
...
- 703
1
vote
0
answers
122
views
Reference/certified data set to compare custom software results
I am currently developing a software application that runs and generates results several statistical tests using .Net libraries. I have been comparing my results to R and another (non free) ...
- 11
-1
votes
1
answer
750
views
How to provide statistical evidence that an experimental method is providing higher mean percentages?
I performed an experiment using two different methods. The data are percentages and higher percentages indicate a better method. The results were as follows:
...
- 11
-1
votes
1
answer
524
views
P values and t statistics? [closed]
I performed an experiment using two different methods on same object, the results of the experiments were
Method 1 70,72,70,75 and 77%
Method 2 80,81,67,75 and 82%
On basis on average I claimed ...
- 11
5
votes
2
answers
1k
views
Comparing P value from t test vs. Mann-Whitney test
If you analyze the same data with a t test and the nonparametric Mann-Whitney test, which do you expect to have the lower P value?
- 21.2k
6
votes
2
answers
8k
views
What to do when the standard error equals 0
I am working on a project where I am evaluating software packages. I have got the results of two experiments where only one variable has been changed. Each experiment has been conducted 10 times. I am ...
- 263
8
votes
4
answers
851
views
Comparing smoke and hormones level in two groups of people. Which test?
I'm totally not a pro in statistics so i hope the question is not too simple!
I have two groups of patients. One group are smokers, the second are non-smokers.
I want to compare the level of some ...
- 2,939
26
votes
4
answers
31k
views
What sense does it make to compare p-values to each other?
I have two populations (men and women), each containing $1000$ samples. For each sample I have two properties A & B (first year grade point average, and SAT score). I have used a t-test separately ...
- 1,820
4
votes
2
answers
1k
views
Is significance more important than absolute value?
I have three groups and I'm comparing two graphs in each group using the t-test:
the absolute difference between two graphs in the first group is 34 with a p=0.024. (*)
The absolute difference in the ...
- 41
9
votes
3
answers
49k
views
Why does t statistic increase with the sample size?
I have a question on reading t-test p-value. If I understand correctly, the t-statistic is computed as:
$t = \frac{\bar{X} - \mu}{\sigma / \sqrt{n}}$
where $\bar{X}$ is sample mean, $\mu$ is ...
- 2,799