# z-test's questions - English 1answer

175 z-test questions.

### 2 Why does it says data should be normally distributed for analysis, when different test follow its own distribution (i.e. t, Z, F)?

Why does it say data should be normally distributed for statistical analysis when different test follow its own distribution (i.e. t, Z, F)? What does normality have to do with this?

### 2 One-Sample z-Test

this is a really simple problem but I'm still in doubt about the solution. There's a population of workers and the goal is to see whether the rate of illegal workers has dropped to 20%. I have a ...

### 1 z test for sum of two percentages as greater than 100

0 answers, 7 views proportion percentage z-test
I have a data set in which participants made a choice between two options--option A and option B. Participants were assigned to either choose an option or reject an option (so, there are two ...

### Comparing Means: Multiple Dependent Variables

1 answers, 820 views t-test manova z-test
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 ...

### 2 lower tail z-test

0 answers, 39 views hypothesis-testing self-study z-test
This is an exercise from Freedman, Pisani and Purves’ Statistics, 4th ed. (p. 552/8) An investigator has independent samples from box A and from box B. Her null hypothesis says that the two boxes ...

### 4 Statistical significance of a difference between poll percentages with a small sample?

Analyzing my company’s internal survey results, I was stuck with calculating statistical difference between percentages. I usually used a Z-test as described below, but I am not sure whether it is ...

### Determining samples sizes for an A/B test using z-test and chi-square test

Assumptions I consider an A/B test where there is a control group and a variant group. Each observation can either be true (converted) or false (not converted). I evenly and randomly split the ...

### 1 Good resources for derivations of statistical significance tests

I am looking for a good resource to deep dive into mathematical derivations of statistical significance tests such as z-test one-sided two-sided t-test pair-wise t-test etc. I can find many ...

### How to do hypothesis testing for two different counts?

I have the following problem: in year A, we observe that a company sold N_A of its product, in year B, we observe that the company sold N_B of its products. How do I do hypothesis testing that the ...

### Simple question about difference of two proportions testing

0 answers, 18 views group-differences z-test
It is usually explained in biostatistics textbooks that to do a z-test for the difference of two proportions, it is necessary that p*n and (1-p)*n are both equal to or above five for both samples. ...

### Calculate Z score from the Confidence level [duplicate]

0 answers, 12 views p-value z-test
How to calculate Z score from the confidence level. I have this small table, but I need the values for all confidence levels (integers from 0-100). Is it possible to somehow calculate the values or ...

### 4 What is wrong with one tailed z-tests for a proportion?

2 answers, 299 views hypothesis-testing proportion z-test
After answering How to analyze observed vs expected when expected is just a proportion? by suggesting that the OP uses a one tail Z-test for their proportion data, I got into a debate in the comments ...

### 1 Z-score computing for two sample proportion comparison

Assume I aggregated the following results: ...

### 2 Required size of control group for two-proportion z test

How do I determine, pre-experiment, the minimum size of a control group that would be needed to satisfy the requirements of a two-proportion z-test? $p_i=\frac{k_i}{n_i}$ is the proportion of ...

### most appropriate statistical test z/t test or Chi square/Fischer exact - Cognition test between genders over period of training?

0 answers, 13 views chi-squared covariance ancova z-test
My data is from four years of students with an equal number of boys and girls of the same age per year chosen. The purpose of the test is to evaluate the influence of training on a certain cognition ...

### 1 Test difference of population proportion and weighted sample proportion

I want to test for differences of the known proportion of the population vs. the proportion of a sample. The sample is weighted by sampling weights. The sum of weights is equal to the size of the ...

### Comparison of regression coefficients

0 answers, 137 views regression z-test
I have run 2 multilevel regression models run on Stata. These models are based on the same sample (hence share the same dependent variable). However, I have 2 different IVs in each model, and the ...

### 1 Hypothesis testing question — how to define the null hypothesis to draw a conclusion

Here is a hypothesis testing question I'm trying to work out but am struggling with how to draw a conclusion, maybe I'm not defining the null hypothesis correctly. The question is as follows: Test ...

### Can I use a Z test?

1 answers, 39 views hypothesis-testing z-test
Can i use a Z test for 2 proportions for the following data? I have 2 samples - male (N=33) and female (N=51) Within the male sample no-one tested positive for a particular attribute. 33 Tested ...

### Can I use z test for a sample that have no outliers?

0 answers, 35 views hypothesis-testing self-study z-test
but I am not sure whether population is normally distributed, standard deviation of population is known. I am measuring national accounts of different countries. Population consists of 183 countries(n=...

### correct test for comparing proportions across groups

1 answers, 21 views t-test fishers-exact z-test
I have 2 overall groups A, B. In both A and B, I have 3 individuals, each scoring a certain percentage on a test. If I want to compare the scores across group A and B, is the correct process to sum ...

### Sample mean Margin of Error and C.I [closed]

I have data on the mean assembly costs for the first n=36 days of production. It is assumed that the following data follows a Normal distribution: ...

### What is the Appropriate Test to Compare Pearson's Correlation Coefficient?

Let say I have this simplified data set which contains four variables (2 categorical, and 2 numerical types): ...

### 1 Z-test or t-test [closed]

0 answers, 34 views hypothesis-testing t-test z-test
A random sample of 1562 undergraduates enrolled in marketing courses was asked to respond on a scale … The sample mean response was 4.27 and the sample standard deviation was 1.32. Test the following ...

### 2 Contradiction between confidence intervals and z-test

I've got a problem with $z$-test and confidence intervals. The $z$-test rejects the null hypothesis (proportions are equal), but the confidence intervals are intersect. Let us consider 2 companies. ...

### Reason for the appropriateness of the z-test for linear regression slope check

0 answers, 46 views regression z-test
I know that the z-test can be used to compare the slopes of two regression lines (lines fitted to two separate data sets). What I do not understand is WHY we can use the z-test for that? Therefore I ...

### What is the method for solving an equation in which a data set is compared with a “standard” with a known mean and variance?

For my homework, I have been asked to solve the following question: Suppose Wal-Mart had to pave over a valuable wetland to make room for a new Super-Store and associated parking lot. In obtaining ...

### Running a 1 Prop Z Test with Time Considered

0 answers, 19 views hypothesis-testing proportion z-test
To start off, I have a machine that communicates Successfully 96% of the time with a standard deviation of 6.32%. This percent is based on previously tabulating its communication success rate for each ...

### 2 two samples, hypothesis test of proportions t or z test

1 answers, 555 views t-test proportion 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 ...

### How to test statistical significance between percentages obtained at two intervals from single sample

I conducted a study on faculty improvement programs, whether they had an impact on teaching practices of faculty members. Sample size was 15. One of the categorical variable observed was 'Is the ...

### 1 One sample proportion test for weighted data

I have a sample of observations (n) representing individual evaluations (positive/negative) of pieces of text (n texts). Each individual can evaluate more texts (thus there are m individuals with m &...

### McNemar or z-test?

I'm doing a matched sample evaluation to see if there is a statistical difference in graduation rates at a college for total sample and sub-groups within the sample after a policy change intended to ...

### 6 Why would one ever use z-score over a t-score?

1 answers, 1.346 views t-test z-test z-statistic
Forgive me if this seems like an elementary question, but no amount of googling has turned up a satisfying answer for me. From what I understand, a t-score should be used instead of a z-score when the ...

### 1 SPSS Categorical Data: Residuals in Crosstabs

I would like to know what's the difference between the standardized residuals and the adjusted standardized residuals in cross-tabs cell display in SPSS? The following definitions are the ones that ...

### Comparing 2 sample proportions from independent populations

1 answers, 50 views proportion z-test
Consider a hypothetical situation, due to a new teaching method being implemented, I want to test whether there is a significant difference in the proportion of students that have passed a particular ...

### 1 comparing 2 population proportions

What are the methods to compare proportions from 2 independent populations i know we can use the z-test or t test for comparing 2 proportions what about Miettinens & Nurimens Liklihood Score ...

### 2 How to test if proportions are the same across categories?

I am working with collision data and want to run a few tests. I thought a chi-square was what I wanted, but it doesn't let me say what I want to. Then I thought a z-test of two proportions was what I ...