# normality

1. R

### Determining ideal sample size, testing normality in SPSS, bonferroni adjustment

Hello all, I am new to the forum. I had a bit of training in statistics and research, particularly statistics in psychology, but I have some basic questions that are holding me back. I would appreciate the help. 1. How can I determine the ideal sample size for a study (upper and lower...
2. ### Justify the use of KS over Shapiro and Wilk normality test

Hello there. I am testing my data distribution for normality using both Shapiro Wilk and Kolmogorov and Smirnov tests in SPSS. S&W reveals that the data is not normally distributed whereas K&S shows its approximately normally distributed. How can i justify the use of K&S over S&W in order to...
3. ### Justify the use of parametric tests on non normally distributed data

Hello there. I have 5 Likert scale questionnaires that have been answered by the same people who have been randomly selected (N=24) and i have the following problem: I first test the data distribution of each scale in order to determine what statistical analysis tests should i employ...
4. ### Transformation didn't normalize the data set... now what?

I study and insect that has a tendency to produce non-normal data sets. I have transformed my current data set using sqrt, sqrt + 0.5, log, log10 and arcsin (even thought this prob isn't appropriate) transformations, but when I check the assumptions on the transformed data set it's still...
5. ### Do I need to worry about normality, if the DV is a 1-item 10point likert scale ?

Dear all, I hope you can help me with the following question My design was a 2 x 2 with a single item measuring responsibility on a 10 point scale as my dv. However, my data is not normally distributed, and a number of standard transformations did not seem to help out here. That's why I was...
6. ### Importance of Normality Assumption for Hypothesis testing methods

Hello everyone! Can someone please share their thoughts on the following question with me. Methods of hypothesis testing usually has a normality assumption for underlying data or for residuals in the case of regression. Why is this assumption important for either case; i.e. for...
7. ### Normality tests and Shape statistics contradictory

Hello. I am testing for normality on a number of repeated measures variables in a sample of 29 people. Both the Kolmogorov-Smirnov test and the Shapiro-Wilk test statistics say that all of these variables are significantly non-normal. However, observations of skew and kurtosis (as well as...
8. ### Fitting of a linea mixed model

Hello I'm trying to modelize the diving depth of birds according to categorical (sex, age class: adults/subadults) and conitnuous parameters (temperature, salinity). The frequecy distribution of this data looks like this: many many many dives between 0-50m deep, some between 50-100m deep and...
9. ### Violation of Normality Assumption in Mixed Design ANOVA

I conducted a study in which two groups of teachers (pre-service and veteran) all watched four video clips of instances of aggression between students. The clips differed by type of aggression and gender of the students depicted (physical vs. relational aggression; male vs. female). After...
10. ### Normality test violations

I have a small sample size (N=26) made up of three groups (n=11, 6 & 9). Whilst running a mixed design ANOVA I have violated both Box's Test of Equality of Covariance (p = .025). I continued my analysis and found that the pre condition also violates Levene's test (p = .016). Is this a...
11. ### To transform or not to transform and how to transform data?

Hi, My study: - 2 groups- 1. Not allowed to work; 2. Allowed to work (control) - compare the groups on various aspects like quality of life, depression, anxiety, etc on standardized quantitative questionnaires - compare if coping ability (2 standardized quantitative scales) predict scores on...
12. ### two groups match or differ on basic demographic variables- how to check?

Hi, My study: - 2 groups- 1. Not allowed to work; 2. Allowed to work (control) - compare the groups on various aspects like quality of life, depression, anxiety, etc on standardized quantitative questionnaires - compare if coping ability (2 standardized quantitative scales) predict scores on...
13. ### Is error rate data normally distributed?

Hi All, I have performed an experiment where I collect the number of 'typing errors' that has occurred. For instance, a user entered 51 different numbers out of which he/she mis-typed 8 numbers. Thus error rate will be (8/51)*100 = 15.68%. Now, I have collected 14 participants' error rate data...
14. ### Confirmatory factor analysis: How to deal with non-normal data

Hello, I have 12 manifest variables, none of which is normally distributed. As far as I know this makes my data unsuitable for a CFA with maximum likelihood estimation (?). I am not sure, however, which alternative estimation method should be used instead. Apart from practical advice I am...
15. ### Data will not normalize & need to run ANOVA

Hello, I have a set of data that I need to run a 2-way ANOVA on. My data is very highly skewed to the right, so it does not follow a normal distribution. I have tried just about every transformation I can find, and cannot get my data to pass the K-S normality test. I wish I could just run a...
16. ### Normality assumption for Regression

I have an outcome variable that is composed of one item on a 3 point scale to assess participation (none-1, member of 1 program-2, member of both programs-3). n=766 The test for normality is significant for the residuals. Is this because the range is too small to be converted to any type of...
17. ### Transformation to improve normality

Hi, I have a problem with some data that I am trying to analyse in a Repeated Measures design. I have 5 conditions (variables), 13 subjects, data points ranging from about -40.0 to +40.0 Both the Kolmogorov-Smirnov and Shapiro-Wilk tests are significant for some of the variables. Some of...
18. ### Non normality in residuals in SLR

Hey guys. I've done a SLR and after testing the residuals for normality using the Shapiro-Wilk test and I've learned that the residuals are not normal. What does this mean? Is the test useless or can it be saved? Should I use another test to test my two variables?
19. ### Odds Ratio Interpretation in Logistic Regression when input is Log-Transformed

Hello, Lets us have a binary dependent variable with 1 as the event and 0 as the non-event. We model the probability of event. The independent variable is income (continuous, interval variable right skewed in 1000 dollars). We take the log of the independent variable and we run the model...
20. ### Regression Analysis - Transformations and Non-Normality

Hello, I am fairly new to regression analysis and have a few questions.. I have a fairly large dataset containing information about 144 municipalities in a country. I am trying to create a model that uses a number of independent variables (urban ratio, literacy rate etc.) to model the...