Questions tagged [t-test]

A test for comparing the means of two samples, or the mean of one sample (or even parameter estimates) with a specified value; also known as the "Student t-test" after the pseudonym of its inventor.

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19 views

Statistical Significance of survey

I recently conducted a survey comparing the generated responses of 2 chatbots. Each participant was asked to complete two tasks: Select a generated response as "best" between 2 generated ...
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Compute-intensive randomized *unpaired* t-test (without paired samples)

Yeh 2000 section 3.3 cites Noreen (1989) and Cohen (1995) for compute-intensive, versions of paired t-tests, which are stonger because they don't make parametric assumptions. However, these tests ...
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Evaluate the increase of a variable (in Likert scale) for a subgroup of the population in a poll

Let's say we do a poll/survey for $n=250$ people, and we study a variable in a Likert scale with 7 possible values (-3 to +3): ...
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Not sure how to start analyzing my dataset- could use any wisdom

I am new to statistics, and while I am not asking for anyone to do anything for me, I would appreciate and use any statistics wisdom that I could get. I was entrusted with some undergraduate research ...
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7 views

Comparing the change in technical coefficients of one sector that received FDI is significantly different compared to change in others that did not

I have datapoints which are technical coefficients (from input output tables) of 10 sectors for 5 years. Some of these have received FDI. I want to check whether the change in the technical ...
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1answer
36 views

Prior distribution on Bayesian T Test?

I have two subgroups of structure (bone structure) and I want to test if there is any difference of size (area) between them, and if there is, how important this difference is. The first set is a ...
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20 views

What is a good location equivalence test for comparison of small and large samples?

I have two one-dimensional samples, one is small (like 2 values) and another of a larger size (several dozens). I want to estimate the probability that the two samples are drawn from different ...
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1answer
31 views

KPSS test: p-value greater than 0.05 but test statistic is less than critical values

I am using Python Statsmodels to find out if my time series is stationary or not. My time series (after the first level shift) passed the ADF test and it suggested that the time series is stationary. ...
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Why the p-value of t.test() is not statistically significant when mean values look really different

I am trying to find out whether there is a significant difference in the mean value of a biomarker between two groups. I am using t.test in R. The ...
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1answer
58 views

Deviation of independence assumption in the t test

How does deviations from the assumption of independence affect the t-test for β1 in linear regression (y=β0+β1x)? How does it affect the null distribution of the test statistic.
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Comparison of 12 measurements in 2019 and 12 measurements in 2020 of the number of individuals in a facility. What is the best method?

I need to compare attendance measurements within the same facility, taken each last day of the month in the year 2019 and the year 2020. So I have 12 measurements in 2019 e 12 measurements in 2020. ...
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How to interpret discrepancy between confidence interval and p-value

My main statistical model returns a significant treatment effect with a p-value below 0.05. Usually, this means that we can reject the null hypothesis that the treatment effect is zero. However, the ...
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1answer
28 views

Appropriate Statistical Test for Likert Data?

I am having trouble deciding the appropriate statistical test to use for a given experiment. In the study, participants first recorded various feelings on a 4 point Likert scale. Ex: How much do you ...
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1answer
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Paired Samples T-Test Assumptions with Ordinal Categorical Data

I would like to check with CrossValidated community whether I interpret the assumptions that are needed to be tested for paired t-test correctly. My questions primarily arise from working with a ...
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27 views

T-test to test if sample comes from the same distribution?

I have a small dataset, sample size of n = 25. These samples form a distribution that looks normally distributed, let's call this distribution Y. I also have a different sample let's call this sample ...
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Paired Hypothesis Testing with Conversion Samples

Let's assume I have 100s of websites on which I am tracking conversion. At some point I change something to all websites. I want to measure if there is a statistical significant difference between my ...
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statistical test to identify the best group of values [closed]

I have very little to no knowledge of stats and hope that you could help me with the problem I am encountering. In brief: I have 5 sets of measurments for different concentration of compounds, using ...
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Why do repeated measures Anova tests and 2-sample dependent t-tests provide the same inference in a case with two treatments?

Why do repeated measures Anova tests and 2-sample dependent t-tests provide the same inference in a case with two treatments? they are different tests but for a case of two treatments somehow they are ...
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multiple one-sample t-test

I'm doing a clinical study with two samples and three repeated measures (duration of treatment: baseline, 10 days and 20 days). I've calculated the difference at 10 and 20 days relative to baseline. ...
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UNEQUAL SAMPLE SIZE ON GENDER [duplicate]

I WANT TO UNDERSTAND IF THERE IS A SIGNIFICANT GENDER DIFFERENCE IN THE COST INCURRED ON REHABILITATION. I HAVE USED STUDENT T-TEST (THOUGH THE RESULT WAS NOT SIGNIFICANT) BUT WAS TOLD THAT T-TEST IS ...
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Independent samples t test for following up missing data - inadequate sample size

I'm running a missing data analysis in SPSS on a data set that examines correlations between an IV and five DVs (all continuous variables). Seven of the participants were inadequately sampled, so I'm ...
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22 views

Statistical significance between two groups of different size

I'm trying to test statistical significance on a sample of two groups that I have, but I'm getting tripped up over the details: I have a sample of 30 days of Group A and Group B. Events in group A and ...
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1answer
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How can I determine if the means between these two small groups are statistically the same?

Group 1: 0.965116667, 0.972716667, 0.821216667, 0.870816667, 0.816216667 Group 2: 1.046016667, 0.794616667, 0.923416667, 0.927816667, 0.780816667, 0.729616667, 0.710816667, 0.788116667, 0.661316667,...
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Find the difference in treatment and control groups during segments of time series data

I have time-series data for a control group and treatment group. I would like to measure the change in current flowing through a cell membrane before and after drug treatment. Each cell is treated ...
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2answers
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How many samples are needed for a T-test

Reading scientific biological papers I can see that comparing two conditions experiments are often repeated 4-6 times when a T-test is applied (for example cell survival is compared between control ...
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Correct Statistical Test for process change

I have a manufacturing process that should result in a 45. I have sampled the output 20 times and recorded the results, made a change and sampled it 20 more times. The goal of the change was to make ...
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Non-parametric comparison of two datasets vs transformed data used in 2 sample t-test

If data is non-normal and less than 40 samples, what is the rationale for using Mann-Whitney vs transformed data in a 2 sample t-test? There is conflicting opinion from various statistical sources ...
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Hypothesis Test: Difference Between Means

I would like to know if I can use a t-test to verify the following hypothesis for the two groups in the chart above: μ1 - μ2 > 0. I am not sure if this test can be used on time series. Tks!
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t test for dependent but unpaired sample

I have two tests on the same groups for students, may be evaluating an education program. If we can paired the same groups of students, this would be paired t-test. But for privacy reasons, so that I ...
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Paired t-test question for spatially distributed data

I have spatially distributed data at 50 locations for pre and post rainfall. So, 2 data points for each station. All the sites are different. Can I use paired t-test on this data?
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2answers
756 views

Significance test for two groups with dichotomous variable

I have a 2x2 table with two independent groups of people that replied Yes or No in the survey: Yes No Group A 350 1250 Group B 1700 3800 Could you help to find a test that can be run on these ...
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6answers
145 views

Comparing two, or more, independent paired t-tests

Can we compare the results from two, or more, independent paired t-tests? For example: I want to test if drug 1 and drug 2 are effective to reduce weight. I have a control group (that will consume a ...
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21 views

Normality assumption check on separate groups vs. on residuals

I was taught in applied stats to verify the assumption of normality on my variables separated by group. For example, if I'm studying a continuous variable like weight (g) in two groups of subjects: A ...
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1answer
43 views

Newey-West (1987) t-stats

I have a time-series which is autocorrelated by construction. I have calculated the sample mean of this time-series, and would like to calculate the t-statistic corresponding to the hypothesis that ...
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11 views

How to do a t-test on rare events distributions?

I have a dataset, which contains several features (feature_1, feature_2, ..., feature_n) and ...
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1answer
40 views

Different notations for cutoff values in statistical tests ($z_{\frac{\alpha}{2}}$ and $t_{\frac{\alpha}{2}}$)

I realize that this question is most likely not too interesting and challenging to discuss here, it's rather a matter of different notations, but I would like to clarify that if possible. When ...
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1answer
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Testing a significance of a specific coefficient in a linear regression with dummy variables and interaction

Consider the following model: $$Y_i = \alpha + \beta X_{i1} + \gamma_1D_{i1} + \gamma_2{D_{i2}} + \delta_{11}(D_{i1}X_{i1}) + \delta_{i2}(D_{i2}X_{i1}) + E_i$$ where $X_{i1}$ is a continuous regressor,...
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14 views

Unusual p-values after weighting

I'm still new to R and most probably this is a rookie question, but maybe some of you could help me understand what is happening. I'm analyzing some results of an experiment in which I have three ...
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3answers
87 views

Why doesn't t-test find a difference between means of two groups when actually there is?

I want to test if the means of two groups of measurements are equal or not. I perform the analysis using R software and, in particular, the function t.test(). Even ...
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unrelated t-test and normal distribution

sorry a bit of a long question here and would appreciate some clarity. so everyone on my psychology course seems to be disagreeing on which statistical test to use for this practical report and now i'...
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13 views

Unusual p-values after weighting

I'm still new to R and most probably this is a rookie question, but maybe some of you could help me understand what is happening. I'm analyzing some results of an experiment in which I have three ...
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0answers
14 views

How to calculate/interpret P-value in one versus two-tailed tests?

I am conducting an ordinal logistic regression and my alternative hypothesis is one-directional (I predict that my independent variable positively affects my dependent variable) and my null hypothesis ...
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21 views

What is the best test for comparing two means of unknown size and standard deviation?

I need to compare a series of means for two unequal student groups (A & B) and need help identifying which test is best to use. I do not have access to the entire data set, just summary ...
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Should I plan my AB testing accordingly to a minimum number of days or to the number of datapoints?

Here's the thing, I was planning to test a new strategy on my website. A typical AB test for a new homepage. One strategy is the current, the control; the other is the variant, the new strategy. I ...
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1answer
35 views

Left tailed t-test in R [closed]

My is $H_0: \beta = 0$ and my $H1: \beta <0$ I want to run a regression in Rstudio and do this with the following command: ...
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1answer
31 views

Correctly using hypothesis testing to conclude X mean is less than Y mean

I have two unknown distributions $A$ and $B$. I drew samples from them and store them in array a and b, respectively. I want to ...
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Is it valid to test if a specified value significantly different from a distribution (reversed concept of one-sample t-test)

The concept of t-test is to test if the mean of a set of samples significantly different from a pre-specified value. If I like to test the opposite: if a pre-specified value (say 19) is significantly ...
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In practice, how would one determine whether to use the assumption unequal or equal variances in a t-test?

I am wondering for the purposes of practicality how one determines whether to use a standard Student's t test or Welch's test for two group means. Is it sufficient to take their empirical standard ...
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1answer
41 views

Looking for the right stats test for my project

I hope someone could help me out and find the appropriate statistics test for my question. I have national incidence rates (per 100,000) before and after a policy change for several countries and I ...
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1answer
31 views

What is the best way to test for a relationship between a binary variable and a continuous variable?

Suppose I have a dataset with a continuous numerical variable $x$ and a binary numerical variable $y$ (with values 0 or 1). How can I test the null hypothesis that the value of $x$ has no effect on ...

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