**175 z-test questions.**

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?

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

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. ...

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 ...

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 ...

Assume I aggregated the following results:
...

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 ...

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 ...

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 ...

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 ...

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 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 ...

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=...

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 ...

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:
...

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

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 ...

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. ...

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 ...

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 ...

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 ...

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 ...

I was wondering how you would calculate the power of a one sided and two sided t test and whether it differed from the z test.
I know for a z test it is $p(z < z_{alpha} - abs(u_{a} - u_0)/(s/sqrt(...

Colleagues, can't wrap my mind on simple question, please help!
I have two products and list of their attributes. My respondents make an answer which product on each attribute they prefer. Finally ...

I've conducted a survey for my thesis where I ask a series of questions of the format:A statement relating to the experimentThen the participants answer ...

I've estimated the age-specific incidence rate ratio of a disease by counting the number of cases in a defined two-year period and divided by the population over those two years for each age group. ...

I'm trying to find out whether there is a statistical method for comparing a distribution of sample proportions to a distribution of population proportions.
For example if I have only two groups, A ...

I have asked a "yes/no" question to a small group of people (n = 22). From the 22, 14 answered "yes" and 8 answered "no". I'd like to find out, with 90% confidence, if the majority of my population (> ...

So I am doing some research in the field of Medical Physics, in particular radiation treatment with photons and protons.
Now, I have two cases I am unsure about.
1) Here I have several patients. ...

I want to test if a quantitative variable is different in 2 groups.
As for what I understood so far, here is the algorithm I should use :
if the length of my 2 subgroups are >30
--> z-test
else, ...

I used my calculator to do a two tailed Z test for two proportions. Here's the data I input:X1 is 834
n1 is 3610
X2 is 145
n2 is 495I chose p1 not equal to ...

Background: I'm giving a presentation to colleagues at work on hypothesis testing, and understand most of it fine but there's one aspect that I'm tying myself up in knots trying to understand as well ...

I am completing a series of questions for this problem and I think I am following but one throws me off.
The problem is a common one:
In a study of smokers who tried to quit smoking with nicotine ...

I have weather stations collecting data (temperature, humidity, solar radiation, wind, etc.) inside and outside low-tech greenhouses. Four of the weather stations are inside, and one is outside. I am ...

I have got 2 large samples and want to compare the difference. There are 2 methods:
Assume the population variances are unknown and unequal, and use the Welch $t$ test.
Assume the population ...

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 ...

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 &...

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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

- hypothesis-testing
- t-test
- proportion
- statistical-significance
- chi-squared
- binomial
- r
- self-study
- regression
- logistic
- normal-distribution
- confidence-interval
- p-value
- power
- mean
- sample-size
- power-analysis
- experiment-design
- generalized-linear-model
- inference
- standard-error
- pearson-r
- ab-test
- mcnemar-test
- probability

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