small sample size

  1. O

    T Test

    Hi T-Test is used instead of Z-Test when we don't know the standard deviation, or when the sample size is too small (less than 31) When we know the standard deviation but the sample size is small, do we use T-Test with sample standard deviation (S)? or T-Test with the known standard deviation...
  2. F

    Sensitivity/Specificity: determining confidence intervals for a small sample size

    I'm conducting a study to determine the validity of a diagnostic test, by comparing its results to a reference standard. The variables I'm dealing with are all categorical. Sadly, I couldn't obtain a proper sample size since the prevalence of the disease is very low (about 6%). When I...
  3. W

    Upper bound for the error on the mean for small samples.

    I have a sample of an unknown distribution for which I would like an estimate of the mean and the error on that mean. For small samples the typical way of doing this breaks down. What is a reasonable way to estimate the mean and an upper bound of the error on the mean? The error on the mean will...
  4. K

    N needed comparing groups in linear regression with many covariates-do I have to few?

    I have two easy, but for me at this point rather devastating, questions I was hoping for one kind hearted or bright individual,or two, to reply on. I'm doing a study with data from a national representative population study. The design is cross-sectional. I've run into serious troubles with...
  5. R

    T-test vs nonparametric for likert scale (very small sample size)

    Hi everyone, I'm in the process of completing my masters thesis, and while I did my share of psych stats in my undergrad it's been YEARS and I'm a lil rusty! Any advice or help anyone could provide would be greatly appreciated, and you may even get a mention in my thesis acknowledgement...
  6. C

    Urgently need help with data analysis

    Hey folks, i really am desperate for help with this, since I have to present my results at a conference in less than two weeks. I am a statistics-noob undergraduate psychoglogy-student, so please go easy on me. Research and Variables I want to examine the correlative relationship between a...
  7. B

    Assigning outliers in very few datapoints

    Hi, I'm a geology PhD student and i have a problem with making my dataset statistically robust. I'm measuring element concentration of my samples using XRF. I have about 900 samples and measured each sample 3 times. Of course there is a variance in these 3 measurements belonging to each...
  8. M

    [non normal Multiple sample comparison] analysis and error bars for medians

    Dear all, Background: Treatment applied to 10 groups of different sizes. Each group treated with a different concentration. Groups 9 and 10 are control/sham and represent the negative outcome. Samples in each group are independent. Group numbers vary from 12 to 4 (I cannot increase the...
  9. G

    Help with statistical analyses with only small sample size and multiple DV's??

    I am looking at the relationship between Schizophrenia, Substance Abuse and Neurocognition. I have 30 P's with Schizophrenia and 30 matched-controls (who are matched on age, gender, education level, IQ, and level of substance use), who have been administered a neurocognitive battery of 11...
  10. J

    (categorical data - small sample) Appropriate test(s)?

    Greetings! I have a small sample (11 responses) of categorical data. I want to compare a binary response (near vs. far) to a nominal response (disease 1,2,3,4,etc.), and see if there is any dependence. Chi-square has given me a poor response with expected cell counts below 1. I looked at...
  11. G

    Very Small Sample Size -What multivariate analysis should be used

    Dear all, Good day! I'm having a hard time researching for possible multivariate analysis to be used in my study. I have less than 10 sample for the study which is already the whole population. I tried to expand by including other cities in my study, yet they immaterially affected the...
  12. B

    CARs from small sample(26): Which Regression is the best to perform?

    Dear All, I am new to this forum, but I am trying to become more and more specified in statistics for my Master Thesis (Erasmus University Rotterdam, Netherlands) Enough intro, my problem is the regression of my sample. I calculated Cumulative Abnormal Returns for 5 event windows, and I...
  13. N

    Likert: Fisher's exact OR Kruskal-Wallis?

    Hi, I've got a survey with 50 responses, and want to test for difference between three subgroups, and strength of association. I'm not happy to treat data as continuous. But I'm not sure whether I should use Kruskal-Wallis to compare rating scores between groups, or Fisher's Exact Test...
  14. B

    Simple question re: correlation?

    Hi, I am looking to assess the correlation between the average costs of services in a geographical region and the average earnings of people in those regions. I would also like to measure the relationship between the percentage change in the cost of those services and the percentage change in...
  15. B

    Independent t test - small sample size - use all data points?

    Hi there, I am running a small study in which both treatment (n = 7) and control groups (n= 6) have undertaken the same 48 item rating scale task (scale = 1 - 10) pre- and post-treatment period. We are running an independent t test to see whether the mean difference score (post test score -...