z-test

  1. G

    Test & Control File Selection - Help

    Hi all I hope all is great with everyone. I'm new on here so sorry to get straight down to my query and hope that someone might be able to point me in the right direction. Thank you. So: I have a prospects direct mail file and I'm testing a new message, (One change). To ensure it’s the...
  2. H

    t-test or z-test for two proportions?

    We did an intervention to reduce the frequency of use of a certain type of treatment and now I want to compare the data pre vs post intervention. For each month I have the number of treatments per 1000 patient visits (because the monthly number of visits fluctuates). I have 6 months of...
  3. Z

    Difference between two independent proportions

    Hello, I am not a statistician, however, for my latest small research, I would like to test whether there is a difference between two independent groups of samples in terms of proportions (one with a condition and one without a condition). I have researched this problem and find out that...
  4. P

    Z Test with unknown sample size

    How would I conduct a z test when I don't have "n"? The instructor never went over what to do without an "n". It has always been provided. Please help me! The national norm for fifth graders on a standardized test of scientific literacy is 37 (σ = 3). Mrs. Jackson determines that the mean...
  5. K

    Column proportion (z-test) is equal to 0 or 1

    I use SPSS custom tables and column proportions (z-test). This is in the output if the column proportion is equal to 0 or 1, "This category is not used in comparisons because its column proportion is equal to zero or one". This happens when 0% or 100% of respondents select an option. When...
  6. R

    How to check whethere there is a difference between 5 samples means

    I have five samples with their means (60, 58, 61.5, 48 and 42) and standard deviations (1, 3, 1.5, 4 and 2) for 3 trials. How to check whether there is a significant difference between these values by statistically.
  7. D

    Two-proportion z test: is it best for my problem, and can I pool data?

    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 to compare two populations -- two genetically different strains of yeast -- to see whether there...
  8. S

    A/B/C Conversion Optimisation

    Hi All, 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. My understanding is that this is a binomial distribution (n=visits, p=conversion...
  9. S

    Formulating a Z-test for a real life problem

    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 to formulate a suitable z-test (or any other suitable test) by which I can test whether the...
  10. E

    Issues with Corsstabulations and Z-tests

    I have been running a number of Crosstabs in SPSS 21 doing Chi-square and Z-tests. It was all going well and making sense until I tried the latest set of cosstabs with predictor variables with large numbers of categories (the dependent variable still only has 2 categories). When I ran the...
  11. L

    Z-test? Paired t-test? T-test two sample assuming equal variances?

    Hey guys! I'm hoping this is the correct forum to post this in. I'm working on my senior thesis, and it's been a while since I've taken stats so I'm hoping you guys can help out. I'm looking at firms following an event and finding the return on their stock price in a set time period. I'm...
  12. G

    How to Calculate Z-score of Binomial Test?

    Hello. I would like to ask how to calculate the z-score of a Binomial test? I am using this http://www.elderlab.yorku.ca/~aaron/Stats2022/BinomialTest.htm link as a reference. I don't get its assumption (second sentence of step 2). I've searched about the formula for this but still I don't...
  13. E

    Z Test of Two Proportions with Small Populations

    This seems like a fairly basic question but is one that I'm having difficulty answering. For comparing two proportions to test for significant differences, I normally use a standard two-proportion Z test. However, I am working on a project that is a special case: we are surveying a very...
  14. I

    Z-Score of Z_Scores... Legitimate Analysis?

    (newbie question...) i have a list of z_Scores for a particular dataset. is it a legitimate to find the z-score of a z-score against a set of z-scores.. so trying to find out how far this particular z-score is compared to a set of z-scores. Anything wrong with this type of analysis? is this...
  15. C

    This is probably easy for you but very hard for me!

    Can someone please help me figure out how to do this problem? A professor knows that from past experience that the time for students to complete a quiz has an N(19, 3) distribution. a. If he allows 20 minutes for the quiz, what percent of the students will not complete the quiz? b...
  16. A

    Comparing Survey Results

    I just recently administered two surveys testing the effectiveness of a product. Each survey consisted of the same 3 questions and were answered on a 10-point Likert scale. Survey A was given to 20 participants before the product was administered and the answers to the questions were as...
  17. A

    z-test?

    Hi, I have satellite imagery for a specific 10km by 20km location for a specific time of year over an 11 year period (2000 to 2010). So 11 images in total. Each image is made up of pixels 250m2 in size which have a value for "greenness" (NDVI). I want to compare greenness in the most...