The z-test is a statistical test for hypothesis testing that uses the standard normal distribution as the sampling distribution of the test statistic. A common example is the test for the difference of two proportions.

learn more… | top users | synonyms

0
votes
0answers
15 views

Proportion z test for predictive model

I have deployed two models, the baseline one which only includes historical data of a stock market index and the twitter model which includes both historical data of the index as well as significant ...
3
votes
1answer
35 views

Testing the Validity of a Test Statistic (incorrectly)

In this post @Wolfgang shares a few lines of code to test in a simulation the ability of a particular test statistic to perform as expected, measured by the percentage of type I errors. He shows by ...
0
votes
0answers
40 views

Z-test and confidence intervals for mutual information

Given two discrete random variables $X,Y$, I would like to obtain confidence intervals for the Mutual Information $I(X;Y)$ and a p-value for the null-hypothesis that $X,Y$ are independent. I would ...
0
votes
0answers
29 views

2-Proportion Z-Test

I want to compare, with 2-proportion Z-Test, the number of student visits to school nurse office in Q1 of 2015 to Q2 of 2015. What do I use for sample size for Q1 and Q2 when it’s different each ...
3
votes
1answer
28 views

Why does changing the null hypothesis change the confidence interval?

Using my stat calculator, I don't see why if I do two different tests with everything the same but the null hypothesis, the confidence interval is different. For example: Has a different CI from ...
4
votes
3answers
128 views

What follows if we fail to reject the null hypothesis?

What conclusions can we draw if $p>\alpha$? Does not rejecting the $H_0$ mean anything?
1
vote
2answers
24 views

Z-test and sampling distribution

The basic trick behind the z-test is the "sampling distribution". The "sampling distribution" is the distribution of all means of all samples. So what we are interested is: if the population means ...
0
votes
0answers
6 views

One variable multiple treatments

I'm drawing a blank on how to analyze this data. I've got one drug/treatment type (variable) with multiple answer options (4 to be exact) and I'd like to compare the answer options for significance. ...
3
votes
1answer
109 views

Statistical comparison between binomial distributions, two groups and many trials

I have a data set with two groups. I have multiple trials with different Ns in each trial, and different numbers of trials for each group. In each trial, for each ...
2
votes
1answer
43 views

Test of proportions or chi-squared? [duplicate]

These data are from an A/B test of free trials to conversion. Someone can sign up for a 30 day free trial of the product. If they like it they stay on and become paying customers. By default (A), ...
2
votes
0answers
47 views

How would I determine statistical significance for ad impressions?

I'm programatically adding keywords to bid on. Some keywords will trigger ads and impressions, and some impressions will trigger clicks. Clicks / impressions = CTR (click-through-rate). Clicks cost. ...
0
votes
1answer
19 views

Test of single proportion - how do i know population proprotion?

I have a study where I did a sample size calculation using N=2800, CI=95%, margin or error = 3.5% to yield n=613. In the study (auditing of charts), I wanted to look at the error rate in my sample. I ...
3
votes
1answer
53 views

Wald Test and Z Test

The "z" hypothesis test is derived from the fact the mean estimator $\hat\Theta$ is distributed normally. If we don't know the variance, we just estimate it ($\widehat{se}$). The Wald test, derived ...
1
vote
1answer
17 views

Proportion test with null hypothesis p1=x*p2

I'd like to compare the proportion of two sets of binomial data where the null hypothesis is not p1=p2, or p1-p2=x, but \begin{equation} H0: p1=x*p2 \end{equation} I've been computing a z test as ...
0
votes
1answer
44 views

Comparing Means: Multiple Dependent Variables

I am using school-level data to compare mean scores for two groups (Group A schools and Group B schools), as measured by a series of indicators: 1) grade-level exam percentile, 2) percent of male ...
1
vote
1answer
57 views

Sample size estimation for test for proportions

I'm interested in finding out if a particular activity increases the chance of a particular segment of prospects converting to a client. I would like to be able to detect a 5% difference in overall ...
2
votes
0answers
26 views

How to compare two PROPORTIONS if you don't have 'n'?

Have data in this format: | A | A' | B | B' | |-----|-----|-----|-----| | 0.4 | 0.2 | 0.4 | 0.3 | | 0.3 | 0.3 | 0.3 | 0.5 | | 0.1 | 0.2 | 0.6 | 0.2 | Note ...
2
votes
1answer
60 views

Exploring a two-way interaction in multi-level regression, why do I get significant contrasts when the confidence intervals overlap on the graph?

I'm exploring a significant two-way interaction in a multi-level random-effects regression. The graph (below) appears to show the interaction is driven by differences at low X, and that at high X the ...
0
votes
0answers
42 views

Comparing differences of ratios in 2 independent populations

I have a setting that I think is quite similar to the one described in What type of statistic should I use to compare ratios in my experiment?. I have two independent populations, which were screened ...
0
votes
1answer
33 views

Z-test with a lot of null values

I have a question concerning the validity of my email tests. I'm testing different email variations (between 2 and 4 variations usually) with different groups of members (hundreds of thousands ...
1
vote
1answer
37 views

Strange two sample z test result in experiment

I performed an experiment on a virtual population wanting to see whether Vitamin C can positively affect performance on an IQ test. I gathered 80 people and grouped them into two groups of 40. ...
1
vote
0answers
169 views

Deriving the power formula of the one-sample proportion test

I have to derive the power of the z-test in testing $$ H_0: \pi=\pi_0 \text{ versus } H_1: \pi>\pi_0 $$ Denoting by $p$ the sample proportion, the power equals $$ ...
2
votes
0answers
24 views

Is there a t-test equivalent to Stouffer's z-test?

I have $k$ pairs of samples from different distributions. For each pair of samples I want to check if the samples are taken from a normal distribution with the same mean and variance. I assume the ...
1
vote
3answers
132 views

“The test statistic is reported as a z…”

I was reading a neuroimaging paper in which the authors compare the effect of a chemical compound on a measure of brain connectivity. They measure the value of connectivity for each brain voxel under ...
0
votes
0answers
56 views

1 sample z test of proportions

We are trying to work out whether what we currently do is accurate. We want to work out if a proportion (% scoring 5 on a 5 point scale) are significantly below a target score. Normally a 1-sample ...
1
vote
1answer
75 views

Significance of continuous variables

I have a table with several numerical continuous measurements and an indicator column catastrophy ...
3
votes
1answer
45 views

Statistics on tastings

Some people at my workplace have had some fun lunch discussion as of late, concerning some people's alleged ability to taste the difference between things one thought one shouldn't be able to taste a ...
2
votes
1answer
251 views

Why is independence required for two- sample proportions z test?

I read in several books as well as in different posts (e.g. here) that independence is required for two-sample proportions z tests. But so far I could not find an explanation why this is the case and ...
1
vote
0answers
101 views

Two-proportion z test: is it best for my problem, and can I pool data from multiple “replicate” populations?

I am examining populations (cultures) of yeast cells and scoring them for a particular trait. The data is categorical; within a population, a yeast cell either has the trait or it does not. I wish ...
2
votes
1answer
125 views

Hypothesis testing for 2 proportions - for A/B testing

I was trying to understand the statistical tests to use during A/B testing and stumbled upon this documentation of the Amazon A/B testing SDK: ...
0
votes
1answer
164 views

Why is P value interpreted under null hypothesis? [duplicate]

P value is explained very nicely in the link . But still i have not understood Why is P value interpreted under null hypothesis?
2
votes
1answer
68 views

Which statistical test should I use to compare two samples?

I have two groups and must conduct hypothesis testing by using an appropriate stats test. Seeing as I have 26 participants in each group, do not have the standard deviation (or any other information ...
0
votes
1answer
36 views

What type of test should be used?

What kind of test would I use to find the answer to this? Is there evidence that cereals promoted in an in-store circular have a higher average number of units sold per store than cereals not ...
2
votes
3answers
53 views

Hypothesis testing - speeds before and after

I have the following data: ...
1
vote
2answers
968 views

two samples z test in Python [closed]

Does Scipy have a z test to compare the mean of two samples? I searched this page but couldn't find one.
0
votes
0answers
10 views

Accuracy Assessment: Do I still have to use any other test statistics?

I have a training set and a separate test set. In both sets, I have extracted two different parameters and I have compared the predicted values of these parameters to the actual values. So, I have ...
0
votes
0answers
121 views

two samples, hypothesis test of proportions t or z test

I have two samples of documents where one sample contains documents of a certain category and another sample contains documents of another category. I am analysing the occurrence of a certain word in ...
0
votes
0answers
56 views

Hypothesis testing with multiple variables

I'm trying to understand the process behind testing both A/B site changes for statistically significant increases in conversion rate, and also how then to expand this to testing multiple variables. ...
0
votes
0answers
32 views

Z test could be a good choice ? and z-test for multiple samples?

I've two samples with mean value $\mu $ and standard deviation $\sigma$ (normal distribution). Can I use a Z-test to compare them ? Also if I don't know the sample size ? If I've five samples to ...
3
votes
0answers
122 views

Permutation for large sample sizes (and z-test)

I was trying to do a permutation test on a large amount of temperature observations in R. Approximately 1700 temperature observations (g1) from one place and 2 ...
0
votes
0answers
60 views

Formulating a Z-test (or any other suitable test ) for survey data

I have a particular survey data related to a particular job. Out of a population of 90 people in this job, 36 people are in the lowest income group. 19 out of 36 people want to quit that job. I want ...
2
votes
0answers
48 views

Difference test for beta–binomial variables

Let $X \sim \textrm{Beta–Binomial}(\alpha_1, \beta_1, n)$ and $Y \sim \textrm{Beta–Binomial}(\alpha_2, \beta_2, n)$ and write $\mu_1 = \frac{\alpha_1}{\alpha_1 + \beta_1}$, $\phi_1 = \alpha_1 ...
2
votes
1answer
38 views

How do we perform a two-tailed z-test when we *do* know the population mean of the intervention sample?

I am in the process of working through the Udacity course Intro to Inferential Statistics. In Lesson 9: Hypothesis Testing, the following example is given. Say that we record survey data from all ...
6
votes
1answer
2k views

chi squared test or Z test? [duplicate]

I have an outcome from a biological experiment, where I have counted the number of dead cells upon a mutation. For example, in once case - out of 120 cells we saw 16% of the dead cells, but our ...
2
votes
1answer
361 views

Are pupils in a school independent and identically distributed when compared to a national population?

I am interested in the way in which data are analysed in education. In England, pupils' reported test results are compared to national test results using z-tests. These results are then used to judge ...
1
vote
2answers
262 views

Large overlap between confidence intervals, although z test for difference was significant

I have calculated a z test to examine the difference between two proportions. I found differences to be significant. The formula I used was: $$z = (p_1-p_2)/SE$$ where $$SE = \sqrt{ p ( 1 - p ) ( ...
1
vote
2answers
261 views

Power calculation of study using 2 sample z-test

This is not homework! I have two very different answers for a power calculation I have done on the below data - ...
0
votes
1answer
160 views

Difference between “common index” and “no common index”

I have been looking at the G*Power tool for Statistical Power Analysis but I am confused by the difference between two of the z-test options. ...
3
votes
2answers
614 views

Why use a z test rather than a t test with proportional data?

When testing the difference between 2 proportions why do we use a z-test rather than a t-test? Further, is there a simple way to conduct an omnibus test for significant differences between more ...
2
votes
1answer
255 views

Comparing sample proportion to population proportion

I have a data set consisting of a number of different hospitals. I am trying to compare the proportion for hospital X to the overall proportion in the data set (which includes hospital X). Should ...