What is P-value: Definition and 31 Discussions

In null hypothesis significance testing, the p-value is the probability of obtaining test results at least as extreme as the results actually observed, under the assumption that the null hypothesis is correct. A very small p-value means that such an extreme observed outcome would be very unlikely under the null hypothesis. Reporting p-values of statistical tests is common practice in academic publications of many quantitative fields. Since the precise meaning of p-value is hard to grasp, misuse is widespread and has been a major topic in metascience.

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  1. F

    I How far and how close to p=0.05 for statistical significance?

    Hello Forum, I understand what the p value represents and how it is calculated in a statistical hypothesis test. In general, the p-value threshold is set to 0.05, i.e. 5% which means that the null hypothesis is reject 5 times our 100 even if it is true. Or that the sample statistics are...
  2. F

    I Proper understanding of p-value

    Hello, I am still slightly confused about the meaning of the p-value. Here my current understanding: There is a population. We don't know its parameters but we want to estimate them. We collect a possibly large sample of size ##n## from it. We formulate the hypotheses ##H0## and ##H1##, set...
  3. Schwann

    I 'Conservative' p-values adjusted

    Hello everyone! Could anybody recommend some strategy of p-values adjustment, as the distribution of my p-values indicates the presence of a big number of false negatives? Usually p-values are adjusted in order to overcome Type 1 errors (e. g. FDR or FWER estimation), but what I need to do is...
  4. P

    MHB Chloe's question via email about a p-value

    I'm assuming the hypothesis test is $\displaystyle H_0 : \mu = 13 \quad \quad H_a : \mu < 13 $ We are given $\displaystyle \mu = 13, \quad \sigma = 2.47, \quad \bar{x} = 12.86 , \quad n = 20 $. The test statistic is $\displaystyle \begin{align*} z &= \frac{\bar{x} -...
  5. A

    MHB Confidence Interval, p-value and Critical Region

    Hello, I have been struggling with this question for a few days now would appreciate being walked through it! :) Data are collected on the wingspans of adult robins. For N=20 birds, the sample mean and variance are given by \overline{x}=9.5cm and s^{2}=2.6^{2}cm^{2} a) If we assume that the...
  6. K

    MHB How to calculate p-value from KS test?

    I've got these tests They show the growth of a plant in mm and I have to test if the growth is superior to 1.1mm I think I have to get the p-value from KS test but I'm not seeing how
  7. T

    I Using interpolation to calculate p-values from t-table?

    Hi there, I've started learning the concept of t-tables and have a question regarding methods to find p-values. I realize that the t-table is limited in providing p-values for every possible t-score. Instead, we must rely on interpolation to attempt to get more precision on the p-value. I've...
  8. CynicusRex

    I Rejecting a null hypothesis without a z-score or p-value?

    Is it possible to reject the null hypothesis without calculating the z-score? We estimated the to be 0.05 —>2* = 0.1; and 2σ = 95% (empirical rule) Therefore there is a 95% confidence interval between 0.95 (=1.05 - 0.1) and 1.15 (=1.05+0.1) So we can say we are 95% confident that the μx (of...
  9. S

    Total significance Higgs discovery at 7+8TeV LHC

    HI guys, a quick question. After the announcement of the discovery of the higgs-like resonance in July 2012 with ~5sigma significance by both ATLAS and CMS, what is the current p-value distribution with the full data set taken into account? And therefore, what is the total significance reached...
  10. S

    Hypothesis testing, P-value, β-error, sample size for β<=0.1

    Homework Statement The life in hours of a battery is known to be normally distributed, with standard deviation of 1.5 hours. A random sample of 12 batteries has a sample mean life time of 50 hours. a) Test the hypothesis that the mean battery life is 50.5 hours (by using α = 0.05). b) What is...
  11. fluidistic

    0.7 correlation but almost 0 p-value, how to interpret?

    Hi guys, I've compared 2 samples of data from which I expected some correlation. The result is that the correlation is about 0.7 while the p-value (calculated by a software) is about ##10^{-92}##. I don't really know how to interpret this low p-value. Does that mean that I can fully trust that...
  12. Kerrie

    Finding the P-Value for Hypothesis Testing

    Homework Statement Suppose a mutual fund qualifies as having moderate risk if the standard deviation of its monthly rate of return is less than 6%. A mutual-fund rating agency randomly selects 28 months and determines the rate of return for a certain fund. The standard deviation of the rate of...
  13. P

    Calculating P-value comparing two percentages of accuracy?

    I have been out of unversity statistics and biometry for a few years do date. I am working in a clical research facility and we are comparing two methods of microbial identification and am now working on the results / charts / statistics. Forgive me for my ignorance, but I am forgetting which...
  14. L

    Calculate P-Value: Compare Method1 vs Method2 Results

    Homework Statement This isn't a homework question but figured this is the best place to ask :) what I have done is measure doses from an x-ray tube at various positions using two different methods, method1 and method2. I would like to say if they are statistically significant or not by using...
  15. V

    Likelihood Ratio Statistic & P-value

    Homework Statement Homework Equations So far I have only worked on question 1, as I was not able to solve it. The likelihood ratio test statistic is defined as follows: λ = 2 Log(L(theta-hat)/L(theta-hat_0)) Where L is the likelihood function, the product of all the pdfs/pmfs, and theta-hat is...
  16. J

    Instead, you should be using the t distribution with 39 degrees of freedom.

    Homework Statement Measure of Contaminatino has a normal distribution w/ unknown mean and unknown variance. Random sample of n=40 provides sample mean = 28.30 and sample variance = 17.38 1)Find Upper 95% Confidence Interval 2)Test Null Hyp = 25.5 vs Alt Hyp = 28.30... Upper Tailed...
  17. J

    Does Chemical Treatment Effectively Reduce Contamination Levels in Waterbodies?

    Homework Statement Binomial Proportion ... In a laboratory experiment, water samples from different waterbodies were examined to check the levels of contamination and were subsequently treated with chemicals for reducing the contamination levels. In one waterbody exposed to...
  18. W

    Understanding P-values in Statistical Analysis

    1. 3. I solved for t distribution = (.03 - 0)/(.1/√25) = .15 P - Value = 2P(T ≥ .15) = 2(.441) = .882. So I got No but instead we fail to reject H0 because 0.882 > .05 (.005 is the typical significance level). Is this correct and would it be a correct interpretation?
  19. N

    When calculating the P-value, must you change the sign of the test statistic?

    Homework Statement When calculating the P-value, must you change the sign of the test statistic depending on the type of test (lower, upper)? For example, if your calculated test statistic is t=2.5 and you want to perform a lower-tailed test, is your answer the cumulative probability of...
  20. P

    Correlation between chi-square and p-value

    Why would a p-value greater than .95 plausibly indicate that the errors/uncertainties were overestimated, i.e. a small chi-square?
  21. N

    How much variance in my p-value

    So l have a nuclear counting system which follows a poisson distribution. I have taken 5 data sets consisting of 30 counts each and l have used them in a chi squared gof test to see if they follow a poisson distribution. For each data set my p-value has been changing. Initially it was 0.5 then...
  22. H

    Calculating P-value from the chi-square test?

    How do we calculate the P-value from the chi-square test? Is their some formula for doing so? I want to do it by hand and not by some online calculator or application.
  23. N

    Kolmogorov-Smirnov and P-value

    So l am testing a sensor l recently developed. I am changing parts on the sensor and testing to see if my data is reproducible with different parts. I compare the data using the KS test. However, the data always have the same distribution or trend line. To test if the two data sets are the same...
  24. C

    Understanding the Uniform Distribution of P-Values in Hypothesis Testing

    I read the following statement from wiki,but I don't know how to get this. "when a p-value is used as a test statistic for a simple null hypothesis, and the distribution of the test statistic is continuous, then the test statistic (p-value) is uniformly distributed between 0 and 1 if the null...
  25. I

    Finding p-value for a Stouffer Z value?

    Hi, just wondering how to find the significance (i.e. the p-value) of a Stouffer Z. Thanks :)
  26. N

    Using a one-sided P-value test in a selection

    Hey guys, I am currently using a one-sided P-value test in a selection between two hypotheses: H0: null hypothesis H1: "signal" hypothesis I know that there are only two possible hypotheses. I have read much in the literature about how the P-value is a bit crappy and a Bayesian model...
  27. N

    Is There a Reliable Bayesian Alternative to the P-Value?

    Dear all, If one has a distribution f(x,mean,sigma), for example the normal distribution, is there a better alternative to the p-value? I have heard many comments that claim the p-value is not to be taken too seriously. Consider that I wish to calculate that probability that x could...
  28. F

    Estimating p-value for Wilcoxon Signed-Rank Test

    I'm trying to estimate the p-value range for a Wilcoxon Signed-Rank Test using a [PLAIN]"www.dekasinthevents.org/images/wtable.jpg"[/URL]. For example: Ho: M1 = M2 Ha: M1 < M2 alpha = 0.05 n = 17 I calculated W = 62 and the rejection region W <= 41. So I would reject Ho. But I'm also...
  29. J

    Critical Value & P-Value Methods: Comparison & Relationships

    1) In the basic probability theory the concepts of mutually exclusive events and independent events share prominent roles, can two events be both mutually exclusive and independent at the same time? 2) What are two vital concepts and the relationship between "Critical Value Method" and the...
  30. M

    Understanding P-Value Confidence in Hypotheses Testing

    I think I'm confused with the concept of the P-Value. Take the hypothesis: Ho: u = 5 Ha: u != 5 And then take another hypothesis: Ho: u = 5 Ha: u > 5 I won't compute the p values, but it is easy to see that with the same statistic test, the p value for the first hypothesis will be...