# Tagged Questions

Statistical significance refers to the probability that, if, in the population from which this sample were drawn the true effect were 0 (or some hypothesized value) a test statistic as extreme or more extreme than the one gotten in the sample could have occurred.

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### How to rank the elements for use in Spearman rank correlation?

If I have 50 items and I want to compare the top 30. I have several cases to do the ranking , so which one is correct? For simplicity I will replace in the example below 50 items with 5 ( A,B,C,D,E) ...
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### which test to use if you only have summary statistics? (non-normal)

Here's the basic problem: visiters to our website were randomly put into one of 7 different groups, and we want to compare the activity of users in the different groups on a downstream site. The ...
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### How to prove that test 1 produces more results than test 2?

If I have 2 tests applied on a set of data, both tests either produce a result ( assume = 1) or no result ( NA , assume = 0 ). Is there a way to prove that test 1 produce more results than test 2 with ...
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### Samples that will result in a large p-value

Consider a one-sample t-test regarding the population mean time to complete a task with a one-sided alternative hypothesis of Ha: μ < 10 minutes. A random sample of times to complete the ...
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### Interpreting p-values

I am a little confused about what p-values mean under Fisher's signficance testing & Neyman-Pearsons hypothesis testing. Fisher uses p-values as a continuous measure of evidence against a null ...
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### Population mean and hypothesis testing

The national average price of a gallon of regular gasoline is 3.71 dollars. Linda would like to assess if the average gas price in her city is significantly higher than the national average. ...
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### Learning about a population mean

Assuming $H_0$ is true, what is the distribution of the test statistic? t(29) Assuming $H_0$ is true, what is the expected value of the test statistic? 87.70 The sample mean of 87.7 was _ standard ...
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### Significance testing question

If 2 distributions of data have the same mean value but standard deviation of sample 1 is twice the value of sample 2, explain what the difference in standard deviation value would indicate about the ...
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### How to compare two survival percentages for two different populations?

I calculated the 5 year survival of two populations keeping different variable constant each time and got percentages. I wanted to determine if these percentages were significantly different from each ...
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### How do I find if there is a significant difference in the number of males and females in a single population?

Also, how do I find if there is a significant difference in the number of males in two populations? In SPSS please!
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### Statistical significance in an underpowered study, false positive?

So, I'm actually a biologist trying to wrap my head around the idea of power of analysis to help design an experiment with the proper sample size. I understand that power of analysis is used to help ...
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### What test of independence of sample proportions is appropriate when n is very large and p is very small?

I have the (not necessarily veridical) impression that typical textbook independence tests of proportions are intended for use the proportions involved are not super small. In my case n may be 10^8 ...
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### Choosing a better data-set

I have two data-sets for same samples. But they are produced using two different instruments. I want to choose one data-set for further analysis. How can I find/prove which data-set is better? To ...
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### What is a meaningful signifcance level when considering a pre-test and post-test model to assess learning in a college course?

When using a pre-test/post-test assessment to measure college learning, what is a meaningful significance level? I realize that p<.05 is the minimum criterion, yet with a correlated-groups t-test, ...
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### Can I trust the result of a one-way ANOVA with many treatments each with very few replicates

I am doing a one-way ANOVA of a response variable (Y) on a treatment factor (T) of 7 levels. However, for each treatment, I have only 2 observations (or replicates). The ANOVA result shows the the ...
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### Spearman rank recommended n size

Is there a recommended n to test for Spearman's rank correlation? I have 2 lists of around 10,000 items. I read that Spearman's rank correlation is fine between 10-30 , can I use spearman to compare ...
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### Significance testing for different groups in multiple regression with dummy-coded interaction variables

Consider a multiple regression predicting outcome Y using a continuous predictor P and an interaction between ...
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### Statistical significance of results in conversion data on group of Adwords keywords

I am trying to optimize my Google Adwords campaign (online advertizing on Google search), and running into the following 'statistical significance' question. I ran a campaign with many keywords ...
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### Determining significant difference between two sets of means

Apologies if this question may have been asked in a different format somewhere else on the site but I'm not much of a statistician and the terminology confuses me somewhat. I'm currently writing a ...
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### Statistical significance of ordered binary vectors

I have a program to predict some values for people. For validation, I keep track of whether the prediction is correct or not, which gives me a binary vector with a length of about 600. To test if it ...
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### Is it possible to have a variable significant in multiple regression but not significant in stepwise regression?

I have run a stepwise regression and found that some of the selected variables are not significant yet in a multiple regression with all variables included in the model those variables were ...
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### What type of statistics to use to show correlation between two discrete sets of data?

I have two variables, each with the same set of 5 unranked possible values (let's call them A/B/C/D/E), and a set of data such as the following (A/A, A/D, B/B, D/D, E/E, B/A etc), where the first ...
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### Can I convert a statistical significance into a zscore using a normal distribution?

Suppose I want to turn statistical significance of 0.05 into a z-score of ~1.64 Can I use a normal distribution to convert these?
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### Standard Error used in Hypothesis Testing and Confidence Interval construction

In the excellent Practical Statistics for Medical Research Douglas Altman writes in page 235: "Because the standard error used for calculating the confidence interval differs from that used in ...
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### What is the explanation for a regressor losing statistical significance when a high leverage point is dropped?

I'm currently working on an Econometrics project and I've come to a point where I've dropped a high leverage point as identified by cook's distance and a leverage plot (had observations that were ...
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### Statistical Difference from Zero

I have a set of data that represents periodic readings. The data shows an upward trend but I need to test for a statistical difference from zero. I believe I should use the t test, two tailed but what ...
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### Enrichment score calculation

I have the following ...
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### Test for whether a change is different in direction for subgroups?

I have a (large) population on which I randomly split into groups, and subjected one group to an experimental condition (call it change A) which demonstrated a significant improvement in a target ...
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### study on multiple outcomes- do I adjust or not adjust p-values?

I did a study comparing 2 groups on multiple outcomes/characteristics. I am still learning the ropes when it comes to statistics, so I failed to specify to adjust the p-values. Some of the results ...
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### Simple multiple choice for test statistic and significance level

A study aims to determine if a new tutoring program (method 1) is better than standard preparatory program (method 2) to prepare students for the SAT. It measures the proportion of students who score ...
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### how to evaluate the importance of different levels of one predictor

This question is a little bit different. Say, I have 4 predictors (all categorical variables with multiple levels), and 1 response variable (binary 0/1). I used a logistic regression model, and found ...
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### Comparing means of three groups

When I want to compare the means between two groups I use a t-test. But how do I check whether the means of three groups are equal or statistically different? E.g. compare the average labour ...
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### How to compare Likert ratings for multiple methods in a usability study

I am designing a questionnaire to compare user experience of usage of a two prototypes of a software - prototype A and B. Users will rate prototype A for a task and then prototype B for performing the ...
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### Which Statistical Test

I have a variable (VAR1 )with two possibilities, let's call them V and N. I asked my experiment participants to detect the VAR1 value. My aim is to compare the correctness rate of answers by ...
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### Finding the z score and p-value of a binomial distribution

Emily is a big fan of lady gaga, and 20% of the songs on her ipod are lady gaga songs. Suppose Emily has her ipod on shuffle and repeat mode, which can be assumed to mean that each song to be played ...
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### Why doesn't this represent a normal approximation to the binomial?

Suppose the registrar's office at a college reports 58% of the students live on campus. An intern working in the administration building is unaware of this 58% parameter value. He designs a study in ...
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### combining binomial and normal values into one significance test

I have conducted an experiment in which a participant completes memory tasks (3 levels, within) while exploring a virtual environment (2 levels, within). The performance on these memory tasks is ...
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### Literature to support effect size over significance

In a large sample (N = 3,265,506 for my study) tests are always significant. Is there an article in the literature I can cite to justify using effect size instead of significance testing?
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### Interpreting significance in hierarchical regression

I've run a Hierarchical Multiple Regression to understand the unique predictive value of three different maternal variables (maternal PTSD, maternal depression, and quality of the parent-child ...
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### How to report significance of a variable that is dependent on two others?

Cost per click is defined by the cost per impression and the click through rate. Given a period of time, divide number of clicks by the sum of the cost per impression for all ads in the same time ...
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### Equations solving and software help for making math patterns

I would like to convert the collected data into mathematical equations by introducing for each requirement by a parameter. In this way, I will get some equations in unknowns. We know a method of ...
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### I want to compare two groups of coin tosses with different number of tosses

I have a list of results of two different groups of coin tosses generated by http://www.wolframalpha.com/input/?i=10+coin+tosses. But the number of tosses is different: There are 10 in one group and ...
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### Finding the test statistic for a majority hypothesis

In a survey of 1070 Ann Arbor residents, 59% supported a ban on bicycles on downtown sidewalks in certain areas with high pedestrian traffic. A city administrator wants to determine if a majority of ...
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### Comparing change in average in two groups: Z-test?

I'm about to start up a project (as a high school teacher) that involves comparing the change in average between two different groups. It's an experiment, and the setup is the following: Obtain a ...
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### How to test (in STATA) whether the gender distribution of employees to jobs differs across two companies?

I have data on several companies where some are headed by a male CEO while others by a female CEO. As you can imagine, the jobs within these companies have different gender compositions. What I am ...
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### Statistical Test for Differences in Groups Based on Multivariate Function/Map

I've recently run into an issue where I am trying to test for a statistical difference between two groups, where each element of a group is itself a data object. For any pair of objects, I can ...
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### Compare means of two groups with a variable that has multiple sub-group

I was unable to understand how to compare multiple mean values in each group. Within the subgroup the mean values influence each other (If one changes, the other changes automatically). I collected ...
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### Frequency data differences test across two groups

I am looking into contrasting two groups with regards to frequency differences over a few time points. To make it clearer: I have for group 1, the frequency difference 5; 4; 1; 2; 3 and for group 2: ...
### Finding parameter $p$ of the Bernouilli distribution which is exactly 99% significant
I ran some experiments first. Afterwards, I looked for the parameter $p_{max}$ for which I can claim the chance a matrix has the ESP-property is $p_{max}$ or lower to a significance of exactly 99%. Is ...