z-scores

  1. O

    Appropriate use of z-scores

    I was thinking about z-scores and I'm curious about their usage when data are skewed/non-normal. I often see zscores being used to identify outliers, e.g. with z>1.96, 2.58, etc. HOWEVER: the z-score calculation of z = (x - mean(x)) / stdev(x) is dependent on the mean, and the mean is not an...
  2. M

    Why autoscale (mean centre and divide by SD) before PLS-DA on integer data?

    I'm currently working with a large dataset of integer data. I'm performing a variable stabilisation transformation on this data and then autoscaling before I begin working with PLS-DA and VIP. Can anyone explain to me why I've had to do this and how it's affecting my data? As I'm unclear myself...
  3. N

    PCA analysis - identifying extremes of each factor

    I am analysing the size and shape of a particular population of people using 25 different body measurements. I completed a PCA/factor analysis in SPSS which suggested 3 factors. The next step is to identify "boundary manikins" that represent the extremes of each factor so I can then...
  4. P

    How to convert two different types of measurement (both in ms) to run a MANOVA?

    I measured reaction time and movement time in an experiment (within-subjects measures) and want to run a MANOVA in SPSS with these measures as the two dependent variables. They are both in milliseconds, but the raw scores are not comparable. My question is how to convert them? Is z-score the...
  5. G

    Z-Scores: Finding the score which separates the top 40% from the bottom 60%?

    Hi there I am struggling a little with my z-scores. This was one of my questions which I do not understand: For a normal distribution with a mean of 100 and an SD of 20, what score separates the top 40% from the bottom 60%? I have no idea how to work this out and have tried google, looking...
  6. C

    z-score within participants before or after averaging conditions

    Hi, I have a Group(2) x Condition(5) ANOVA design. Group is a between factor and Condition is within. I'm specifically interested in interaction effects (not overall group differences). I want to z-standardize the data within each participant to account for inter-individual differences...
  7. D

    Structural Equation Modeling: When and why do you use Z-scores instead of Mean.

    Hi. Can anyone help me answer the question why some people who do SEM use z-scores as opposed to using mean scores? (articles and books are welcomed) Thank you.
  8. R

    Use z-scores in Repeated Measures ANCOVA?

    Hi everyone, My dissertation has participants answer three questions at four different timepoints in a video. For each timepoint, I have averaged the three questions for an average response per timepoint (4 scores). I also have a dichotomous between subjects variable, and two continuous...
  9. K

    Hypothesis tests applied to two means (two related samples) question about null.

    Hello, I am currently studying for an midterm, and am running into a roadblock with some of the concepts concerning hypothesis testing applied to means with two related samples. I am noticing in all of the examples in the textbook that the null hypothesis (mu) is always Ho = 0. Why is it that...
  10. S

    Using z-scores and ANOVA?

    Hello helpful people, I am wondering whether I can use z-scores to analyse variance and compare means - as though they were raw scores. The project: Participants are divided into 4 different intervention conditions. I have pre- and post-intervention anxiety and depression scores, however...
  11. H

    need help drawing matched controls group

    Hello, I am doing a study on schizophrenia and cannabis use. I currently have a group of 35 schizophrenia patients who have a history of cannabis use and need to recruit a matched healthy normal control group for comparison. I was wondering if u had any information on drawing a matched...