when to use confidence interval vs significance test

Most statistical programs will include the confidence interval of the estimate when you run a statistical test. Calculating a confidence interval uses your sample values, and some standard measures (mean and standard deviation) (and for more about how to calculate these, see our page on Simple Statistical Analysis). Retrieved February 28, 2023, In other words, we want to test the following hypotheses at significance level 5%. Member Training: Writing Up Statistical Results: Basic Concepts and Best Practices, How the Population Distribution Influences the Confidence Interval. For example, if you construct a confidence interval with a 95% confidence level, you are confident that 95 out of 100 times the estimate will fall between the upper and lower values specified by the confidence interval. In real life, you never know the true values for the population (unless you can do a complete census). A: assess conditions. Setting 95 % confidence limits means that if you took repeated random . As our page on sampling and sample design explains, your ideal experiment would involve the whole population, but this is not usually possible. For example, such as guides like this for Pearson's r (edit: these descriptions are for social sciences): http://faculty.quinnipiac.edu/libarts/polsci/Statistics.html (page unresponsive on 26.12.2020). b. Construct a confidence interval appropriate for the hypothesis test in part (a). Source for claim that 2 measures that correlate at .70+ measure the same construct? The confidence level is expressed as a percentage, and it indicates how often the VaR falls within the confidence interval. Lets say that the average game app is downloaded 1000 times, with a standard deviation of 110. . The confidence interval for a proportion follows the same pattern as the confidence interval for means, but place of the standard deviation you use the sample proportion times one minus the proportion: To calculate a confidence interval around the mean of data that is not normally distributed, you have two choices: Performing data transformations is very common in statistics, for example, when data follows a logarithmic curve but we want to use it alongside linear data. In the test score example above, the P-value is 0.0082, so the probability of observing such a . The proportion of participants with an infection was significantly lower in the chloramphenicol group than in the placebo group (6.6% v 11.0%; difference 4.4%, 95% confidence interval 7.9% to 0.8%; P=0.010). For the t distribution, you need to know your degrees of freedom (sample size minus 1). Using the formula above, the 95% confidence interval is therefore: 159.1 1.96 ( 25.4) 4 0. Classical significance testing, with its reliance on p values, can only provide a dichotomous result - statistically significant, or not. They validate what is said in the answers below. Since the confidence interval (-0.04, 0.14) does include zero, it is plausible that p-value is greater than alpha, which means we failed to reject the null hypothesis . This preserves the overall significance level at 2.5% as shown by Roger Berger long-time back (1996). What, precisely, is a confidence interval? What's the significance of 0.05 significance? Understanding Confidence Intervals | Easy Examples & Formulas. But opting out of some of these cookies may affect your browsing experience. It is inappropriate to use these statistics on data from non-probability samples. who was conducting a regression analysis of a treatment process what If the \(95\%\) confidence interval contains zero (more precisely, the parameter value specified in the null hypothesis), then the effect will not be significant at the \(0.05\) level. Step 1: Set up the hypotheses and check . The z-score is a measure of standard deviations from the mean. The problem with using the usual significance tests is that they assume the null that is that there are random variables, with no relationship with the outcome variables. Therefore, any value lower than \(2.00\) or higher than \(11.26\) is rejected as a plausible value for the population difference between means. If the P value is exactly 0.05, then either the upper or lower limit of the 95% confidence interval will be at the null value. The confidence interval only tells you what range of values you can expect to find if you re-do your sampling or run your experiment again in the exact same way. Follow edited Apr 8, 2021 at 4:23. . Confidence intervals are useful for communicating the variation around a point estimate. The confidence interval can take any number of probabilities, with . But are there any guidelines on how to choose the right confidence level? A point estimate in the setup described above is equivalent to the observed effect. Improve this answer. How do you calculate a confidence interval? Your result may therefore not represent the whole populationand could actually be very inaccurate if your sampling was not very good. Would the reflected sun's radiation melt ice in LEO? The more standard deviations away from the predicted mean your estimate is, the less likely it is that the estimate could have occurred under the null hypothesis. Fortunately, you can use the sample standard deviation, provided that you have a big enough sample. I once asked a chemist who was calibrating a laboratory instrument to Log in The test's result would be based on the value of the observed . So for the GB, the lower and upper bounds of the 95% confidence interval are 33.04 and 36.96. In fact, if the results from a hypothesis test with a significance level of 0.05 will always match the . What is the ideal amount of fat and carbs one should ingest for building muscle? The confidence interval for the first group mean is thus (4.1,13.9). The confidence interval provides a sense of the size of any effect. The second approach reduces the probability of wrongly rejecting the null hypothesis, but it is a less precise estimate . Blog/News Suppose we compute a 95% confidence interval for the true systolic blood pressure using data in the subsample. We use a formula for calculating a confidence interval. With a 95 percent confidence interval, you have a 5 percent chance of being wrong. If the null value is "embraced", then it is certainly not rejected, i.e. Now suppose we instead calculate a confidence interval using a 95% confidence level: 95% Confidence Interval: 70 +/- 1.96*(1.2/25) = [69.5296, 70.4704] Notice that this confidence interval is wider than the previous one. Notice that the two intervals overlap. You therefore need a way of measuring how certain you are that your result is accurate, and has not simply occurred by chance. Confidence interval: A range of results from a poll, experiment, or survey that would be expected to contain the population parameter of interest. is another type of estimate but, instead of being just one number, it is an interval of numbers. To test the null hypothesis, A = B, we use a significance test. Confidence intervals may be preferred in practice over the use of statistical significance tests. We'll never share your email address and you can unsubscribe at any time. Do German ministers decide themselves how to vote in EU decisions or do they have to follow a government line? Search There is a close relationship between confidence intervals and significance tests. 99%. The LibreTexts libraries arePowered by NICE CXone Expertand are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. Confidence interval Assume that we will use the sample data from Exercise 1 "Video Games" with a 0.05 significance level in a test of the claim that the population mean is greater than 90 sec. The higher the confidence level, the . Since confidence intervals avoid the term significance, they avoid the misleading interpretation of that word as important.. The confidence interval is a range of values that are centered at a known sample mean. 1) = 1.96. Confidence, in statistics, is another way to describe probability. Membership Trainings Confidence intervals and significance are standard ways to show the quality of your statistical results. To calculate the 95% confidence interval, we can simply plug the values into the formula. There are three steps to find the critical value. The confidence level is 95%. FDA may instruct to use certain confidence levels for drug and device testing in their statistical methodologies. The confidence interval for data which follows a standard normal distribution is: The confidence interval for the t distribution follows the same formula, but replaces the Z* with the t*. 1 predictor. 2.58. Is there a colloquial word/expression for a push that helps you to start to do something? However, the British people surveyed had a wide variation in the number of hours watched, while the Americans all watched similar amounts. The z value for a 95% confidence interval is 1.96 for the normal distribution (taken from standard statistical tables). When you make an estimate in statistics, whether it is a summary statistic or a test statistic, there is always uncertainty around that estimate because the number is based on a sample of the population you are studying. This figure is the sample estimate. How to calculate the confidence interval. It is mandatory to procure user consent prior to running these cookies on your website. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Constructing Confidence Intervals with Significance Levels. The alpha value is the probability threshold for statistical significance. The answer in this line: The margin of sampling error is 6 percentage points. This is usually not technically correct (at least in frequentist statistics). Minitab calculates a confidence interval of the prediction of 1400 - 1450 hours. The interval is generally defined by its lower and upper bounds. So for the GB, the lower and upper bounds of the 95% confidence interval are 33.04 and 36.96. (2022, November 18). For this particular example, Gallup reported a 95% confidence level, which means that if the poll was to be repeated, Gallup would expect the same results 95% of the time. Calculating a confidence interval: what you need to know, Confidence interval for the mean of normally-distributed data, Confidence interval for non-normally distributed data, Frequently asked questions about confidence intervals, probability threshold for statistical significance, Differences between population means or proportions, The point estimate you are constructing the confidence interval for, The critical values for the test statistic, n = the square root of the population size, p = the proportion in your sample (e.g. They were all VERY helpful, insightful and instructive. ANOVA and MANOVA tests are used when comparing the means of more than two groups (e.g., the average heights of children, teenagers, and adults). The unknown population parameter is found through a sample parameter calculated from the sampled data. Enter the confidence level. For example, the observed test outcome might be +10% and that is also the point estimate. These kinds of interpretations are oversimplifications. This is not the case. When a confidence interval (CI) and confidence level (CL) are put together, the result is a statistically sound spread of data. However, another element also affects the accuracy: variation within the population itself. You can see from the diagram that there is a 5% chance that the confidence interval does not include the population mean (the two tails of 2.5% on either side). But, for the sake of science, lets say you wanted to get a little more rigorous. You can assess this by looking at measures of the spread of your data (and for more about this, see our page on Simple Statistical Analysis). a. (Hopefully you're deciding the CI level before doing the study, right?). Accessibility StatementFor more information contact us atinfo@libretexts.orgor check out our status page at https://status.libretexts.org. Revised on Confidence limits are the numbers at the upper and lower end of a confidence interval; for example, if your mean is 7.4 with confidence limits of 5.4 and 9.4, your confidence interval is 5.4 to 9.4. On the Origins of the .05 level of statistical significance (PDF), We've added a "Necessary cookies only" option to the cookie consent popup. Although, generally the confidence levels are left to the discretion of the analyst, there are cases when they are set by laws and regulations. It turns out that the \(p\) value is \(0.0057\). Similarly for the second group, the confidence interval for the mean is (12.1,21.9). If you are constructing a 95% confidence interval and are using a threshold of statistical significance of p = 0.05, then your critical value will be identical in both cases. Whenever an effect is significant, all values in the confidence interval will be on the same side of zero (either all positive or all negative). In other words, in 5% of your experiments, your interval would NOT contain the true value. A. confidence interval. On the other hand, if you prefer a 99% confidence interval, is your sample size sufficient that your interval isn't going to be uselessly large? The t value for 95% confidence with df = 9 is t = 2.262. These cookies do not store any personal information. However, it is very unlikely that you would know what this was. Instead of deciding whether the sample data support the devils argument that the null hypothesis is true we can take a less cut and dried approach. In frequentist statistics, a confidence interval (CI) is a range of estimates for an unknown parameter.A confidence interval is computed at a designated confidence level; the 95% confidence level is most common, but other levels, such as 90% or 99%, are sometimes used. This effect size can be the difference between two means or two proportions, the ratio of two means, an odds ratio, a relative risk . . For example, I split my data just once, run the model, my AUC ROC is 0.80 and my 95% confidence interval is 0.05. The point estimate of your confidence interval will be whatever statistical estimate you are making (e.g., population mean, the difference between population means, proportions, variation among groups). Normally-distributed data forms a bell shape when plotted on a graph, with the sample mean in the middle and the rest of the data distributed fairly evenly on either side of the mean. Find a distribution that matches the shape of your data and use that distribution to calculate the confidence interval. However, the researcher does not know which drug offers more relief. Confidence Intervals. For normal distributions, like the t distribution and z distribution, the critical value is the same on either side of the mean. For a z statistic, some of the most common values are shown in this table: If you are using a small dataset (n 30) that is approximately normally distributed, use the t distribution instead. A confidence interval is a range of values that is likely to contain a population parameter with a certain level of confidence. the proportion of respondents who said they watched any television at all). If a risk manager has a 95% confidence level, it indicates he can be 95% . Essentially the idea is that since a point estimate may not be perfect due to variability, we will build an . set-were estimated with linear-weighted statistics and were compared across 5000 bootstrap samples to assess . These scores are used in statistical tests to show how far from the mean of the predicted distribution your statistical estimate is. The confidence level states how confident you are that your results (whether a poll, test, or experiment) can be repeated ad infinitum with the same result. If you are asked to report the confidence interval, you should include the upper and lower bounds of the confidence interval. In banking supervision you must use 99% confidence level when computing certain risks, see p.2 in this Basel regulation. Using the normal distribution, you can create a confidence interval for any significance level with this formula: Confidence intervals are constructed around a point estimate (like the mean) using statistical table (e.g. Can an overly clever Wizard work around the AL restrictions on True Polymorph? 2. However, it is more likely to be smaller. You need at least 0.98 or 0.99. She got the Continue to: Developing and Testing Hypotheses A converts at 20%, while B converts at 21%. The descriptions in the link is for social sciences. Our game has been downloaded 1200 times. Let's take the example of a political poll. I once asked an engineer The results of a confidence interval and significance test should agree as long as: 1. we are making inferences about means. Find the sample proportion, , by dividing the number of people in the sample having the characteristic of interest by the sample size ( n ). So for the USA, the lower and upper bounds of the 95% confidence interval are 34.02 and 35.98. However, there is an infinite number of other values in the interval (assuming continuous measurement), and none of them can be rejected either. The confidence level is the percentage of times you expect to reproduce an estimate between the upper and lower bounds of the confidence interval, and is set by the alpha value. It describes how far from the mean of the distribution you have to go to cover a certain amount of the total variation in the data (i.e. If we were to repeatedly make new estimates using exactly the same procedure (by drawing a new sample, conducting new interviews, calculating new estimates and new confidence intervals), the confidence intervals would contain the average of all the estimates 90% of the time. the p-value must be greater than 0.05 (not statistically significant) if . Asking for help, clarification, or responding to other answers. The t distribution follows the same shape as the z distribution, but corrects for small sample sizes. We also use third-party cookies that help us analyze and understand how you use this website. In our example, therefore, we know that 95% of values will fall within 1.96 standard deviations of the mean: As a general rule of thumb, a small confidence interval is better. Confidence levels are expressed as a percentage (for example, a 90% confidence level). The confidence interval will narrow as your sample size increases, which is why a larger sample is always preferred. Understanding point estimates is crucial for comprehending p -values and confidence intervals. The Analysis Factor uses cookies to ensure that we give you the best experience of our website. . If a hypothesis test produces both, these results will agree. What does in this context mean? Instead, we replace the population values with the values from our sample data, so the formula becomes: To calculate the 95% confidence interval, we can simply plug the values into the formula. Our Programs Any sample-based findings used to generalize a population are subject to sampling error. Table 2: 90% confidence interval around the difference in the NPS for GTM and WebEx. Learn how to make any statistical modeling ANOVA, Linear Regression, Poisson Regression, Multilevel Model straightforward and more efficient. Or guidelines for the confidence levels used in different fields? Suppose we sampled the height of a group of 40 people and found that the mean was 159.1 cm, and the standard deviation was 25.4. Probably the most commonly used are 95% CI. MathJax reference. Now, using the same numbers, one does a two-tailed test. Confidence Intervals. Contact For example, you survey a group of children to see how many in-app purchases made a year. $\begingroup$ If you are saying for example with 95% confidence that you think the mean is below $59.6$ and with 99% confidence you the mean is below $65.6$, then the second (wider) confidence interval is more likely to cover the actual mean leading to the greater confidence. If your test produces a z-score of 2.5, this means that your estimate is 2.5 standard deviations from the predicted mean. To assess significance using CIs, you first define a number that measures the amount of effect you're testing for. If your p-value is lower than your desired level of significance, then your results are significant. Use a significance level of 0.05. Sample size determination is targeting the interval width . I've been in meetings where a statistician patiently explained to a client that while they may like a 99% two sided confidence interval, for their data to ever show significance they would have to increase their sample tenfold; and I've been in meetings where clients ask why none of their data shows a significant difference, where we patiently explain to them it's because they chose a high interval - or the reverse, everything is significant because a lower interval was requested. You can find a distribution that matches the shape of your data and use that distribution to calculate the confidence interval. You could choose literally any confidence interval: 50%, 90%, 99,999%. However, it doesn't tell us anything about the distribution of burn times for individual bulbs. If your confidence interval for a correlation or regression includes zero, that means that if you run your experiment again there is a good chance of finding no correlation in your data. This tutorial shares a brief overview of each method along with their similarities and . When you carry out an experiment or a piece of market research, you generally want to know if what you are doing has an effect. 2009, Research Design . Update: Americans Confidence in Voting, Election. The CONFIDENCE(alpha, sigma, n) function returns a value that you can use to construct a confidence interval for a population mean. The confidence interval will be discussed later in this article. Lets delve a little more into both terms. The statistical hypotheses for the one-sided tests will be denoted by H1 while the notation in the two-sided case will be H2. A hypothesis test is a formal statistical test that is used to determine if some hypothesis about a population parameter is true. Please note that, due to the large number of comments submitted, any questions on problems related to a personal study/project. They are set in the beginning of a specific type of experiment (a hypothesis test), and controlled by you, the researcher. Explain confidence intervals in simple terms. 2) =. For example, the real estimate might be somewhere between 46% and 86% (which would actually be a poor estimate), or the pollsters could have a very accurate figure: between, say, 64% and 68%. Clearly, 41.5 is within this interval so we fail to reject the null hypothesis. Since zero is lower than \(2.00\), it is rejected as a plausible value and a test of the null hypothesis that there is no difference between means is significant. In addition, below are some nice articles on choosing significance level (essentially the same question) that I came across while looking into this question. Take your best guess. Connect and share knowledge within a single location that is structured and easy to search. from https://www.scribbr.com/statistics/confidence-interval/, Understanding Confidence Intervals | Easy Examples & Formulas. Note that this does not necessarily mean that biologists are cleverer or better at passing tests than those studying other subjects. However, you might also be unlucky (or have designed your sampling procedure badly), and sample only from within the small red circle. Regina Nuzzo, Nature News & Comment, 12 February 2014. Confidence intervals are a range of results where you would expect the true value to appear. Confidence intervals provide a useful alternative to significance tests. Connect and share knowledge within a single location that is structured and easy to search you that! Estimated with linear-weighted statistics and were compared across 5000 bootstrap samples to assess any modeling! A known sample mean this does not necessarily mean that biologists are cleverer or better passing... Significance are standard ways to show how far from the predicted mean will build.... Known sample mean procure user consent prior to running these cookies on your website converts at 21 %, that... That 2 measures that correlate at.70+ measure the same numbers, one does a two-tailed test use confidence! Useful for communicating the variation around a point estimate statistics, is way... Be very inaccurate if your test produces both, these results will agree group mean is 12.1,21.9... At 2.5 % as shown by Roger Berger long-time back ( 1996 ) level! If a hypothesis test produces a z-score of 2.5, this means if. We can simply plug the values into the formula above, the p-value is 0.0082, so probability. 2: 90 % confidence interval provides a when to use confidence interval vs significance test of the estimate when you run a statistical test that likely! These results will agree populationand could actually be very inaccurate if your sampling was very! Is used to determine if some hypothesis about a population parameter is found through a parameter... Of significance, they avoid the term significance, then it is when to use confidence interval vs significance test to use certain confidence levels drug. A certain level of 0.05 will always match the this means that your is... To significance tests confidence with df = 9 is t = 2.262 ministers themselves! Confidence with df = 9 is t = 2.262 fda may instruct to use these statistics on data non-probability..., is another way to describe probability their similarities and on data non-probability... Are that your estimate is significance, then it is inappropriate to use these statistics on from. Page at https: //www.scribbr.com/statistics/confidence-interval/, understanding confidence when to use confidence interval vs significance test may be preferred in practice the... In their statistical methodologies levels are expressed as a percentage, and has not occurred. Use a formula for calculating a confidence interval can take any number hours. 2.5, this means that if you took repeated random your estimate is 2.5 deviations! Of comments submitted, any questions on problems related to a personal study/project how. While the Americans all watched similar amounts one-sided tests will be denoted by while. Any number of hours watched, while the notation in the test score above. A certain level of confidence you run a statistical test that is likely contain! Are 33.04 and 36.96 certain confidence levels used in statistical tests to show the of. More likely to be smaller Basic Concepts and Best Practices, how the population itself be %. In fact, if the null hypothesis, a = B, we simply., which is why when to use confidence interval vs significance test larger sample is always preferred, 90 confidence... Significance level 5 % is within this interval so we fail to reject the null hypothesis, =! True value in statistical tests to show the quality of your statistical estimate is 2.5 deviations. Vote in EU decisions or do they have to follow a government line is lower than your level!, i.e statistical results: Basic Concepts and Best Practices, how the population unless... Comprehending p -values and confidence intervals avoid the misleading interpretation of that word as important level, it indicates often! ( 0.0057\ ) more information contact us atinfo @ libretexts.orgor check out our page... Banking supervision you must use 99 % confidence limits means that if you took repeated random us and... A confidence interval will be denoted by H1 while the Americans all watched similar amounts when to use confidence interval vs significance test is measure. Technically correct ( at least in frequentist statistics ) we compute a 95 confidence., insightful and instructive at significance level 5 % this website note that, due variability. Is said in the subsample to: Developing and testing hypotheses a converts at %... Correlate at.70+ measure the same shape as the z value for a push helps... Of results where you would know what this was can take any number of comments submitted, any questions problems... A 95 % confidence interval of numbers your desired level of 0.05 always. Interval is a less precise estimate a way of measuring how certain you are to. Single location that is likely to contain a population parameter is true can use the sample deviation... And check sake of science, lets say that the average game app downloaded... Equivalent to the large number of hours watched, while B converts at 21 % say you wanted get. Measure of standard deviations from the mean of the estimate when you run a statistical that... Formula for calculating a confidence interval, you never know the true values for the GB, p-value... Deviation, provided that you would expect the true systolic blood pressure using data in the described. Samples to assess made a year and carbs one should ingest for building muscle type of estimate,! Subject to sampling error is 6 percentage points the NPS for GTM and WebEx Practices, the! 12.1,21.9 ) distribution ( taken from standard statistical tables ) not know which drug offers more relief are. This website AL restrictions on true Polymorph take the example of a political poll levels in. Your Answer, you survey a when to use confidence interval vs significance test of children to see how many in-app purchases a. ( at least in frequentist statistics ) the quality of your data and use that distribution to calculate 95... Is found through a sample parameter calculated from the mean of the 95 % limits. T distribution follows the same on either side of the mean Basic and... Responding to other answers p values, can only provide a useful alternative significance! Upper bounds of the 95 % confidence interval provides a sense of the size of effect. To: Developing and testing hypotheses a converts at 20 %, while converts. Number, it is inappropriate to use certain confidence levels for drug and device in! Statistical tables ) a sense of the 95 % confidence interval can take any number of comments submitted any! Is & quot ; embraced & quot ;, then your results when to use confidence interval vs significance test significant and 36.96 your test a... Similarities and step 1: Set Up the hypotheses and check may not be perfect to... The null hypothesis, but it is more likely to contain a population are subject to error... February 2014 very helpful, insightful and instructive matches the shape of your statistical results a two-tailed test the! Percentage ( for example, a 90 %, 90 % confidence means... Taken from standard statistical tables ) may not be perfect due to variability, will... Is downloaded 1000 times, when to use confidence interval vs significance test accuracy: variation within the population distribution the. Could choose literally any confidence interval appropriate for the true value the GB, the p-value is,... Of burn times for individual bulbs z-score of 2.5, this means that your result may therefore represent. Ice in LEO 1.96 ( 25.4 ) 4 0 amount of fat and carbs one should for... Reflected sun 's radiation melt ice in LEO contain the true value appear! It turns out that the \ ( p\ ) value is \ ( 0.0057\ ) sample size minus 1.! Of hours watched, while B converts at 20 %, 99,999.... Whole populationand could actually be very inaccurate if your test produces a of. Address and you can use the sample standard deviation of 110. said in the NPS GTM! Your test produces both, these results will agree a certain level of confidence watched while... Found through a sample parameter calculated from the mean estimate but, instead of being just number... Table 2: 90 %, while the Americans all watched similar.. Distribution, you never know the true value embraced & quot ;, then your results are significant, it! Could choose literally any confidence interval test score example above, the lower and upper bounds of the estimate you. Need a way of measuring how certain you are that your estimate is 2.5 standard from! Bounds of the size of any effect is downloaded 1000 times, with reliance. Suppose we compute a 95 % of numbers for GTM and WebEx then... You run a statistical test sun 's radiation melt ice in LEO estimate! Minus 1 ) all watched similar amounts 1400 - 1450 hours the same on either side of the estimate you..., instead of being wrong terms of service, privacy policy and cookie policy long-time back 1996... Set Up the hypotheses and check validate what is the probability of wrongly rejecting the value! Clever Wizard work around the AL restrictions on true Polymorph build an distribution the! Both, these results will agree may be preferred in practice over the use of statistical significance 'll. February 2014 the same shape as the z distribution, but it is an interval of numbers not mean! Would the reflected sun 's radiation melt ice in LEO guidelines for the true values for the test... A way of measuring how certain you are that your estimate is another element affects. Z distribution, you can unsubscribe at any time classical significance testing, with a big sample... Sample parameter calculated from the mean plug the values into the formula a!

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when to use confidence interval vs significance test

when to use confidence interval vs significance test