scholarly journals Additional file to "Why Psychologists Should by Default Use Welch's t-test Instead of Student's t-test." (in press for the International Review of Social Psychology)

2017 ◽  
Author(s):  
Marie Delacre ◽  
Daniel Lakens ◽  
Christophe Leys
Keyword(s):  
Psychological Research ◽  
Error Rates ◽  
T Test ◽  
International Review ◽  
Type 1 Error ◽  
Statistical Inferences ◽  
Homogeneity Of Variance ◽  
Student’S T ◽  
Student’S T Test

When comparing two independent groups, researchers in Psychology commonly use Student’s t-test. Assumptions of normality and of homogeneity of variance underlie this test. More often than not, when these conditions are not met, Student’s t-test can be severely biased, and leads to invalid statistical inferences. Moreover, we argue that the assumption of equal variances will seldom hold in psychological research and that choosing between Student’s t-test or Welch’s t-test based on the outcomes of a test of the equality of variances often fails to provide an appropriate answer. We show that the Welch’s t-test provides a better control of Type 1 error rates when the assumption of homogeneity of variance is not met, and loses little robustness compared to Student’s t-test when the assumptions are met. We argue that Welch’s t-test should be used as a default strategy.

scholarly journals Why Psychologists Should by Default Use Welch's t-test Instead of Student's t-test (in press for the International Review of Social Psychology).

2017 ◽  
Author(s):  
Marie Delacre ◽  
Daniel Lakens ◽  
Christophe Leys
Keyword(s):  
Psychological Research ◽  
Error Rates ◽  
T Test ◽  
International Review ◽  
Type 1 Error ◽  
Statistical Inferences ◽  
Homogeneity Of Variance ◽  
Student’S T ◽  
Student’S T Test

When comparing two independent groups, researchers in Psychology commonly use Student’s t-test. Assumptions of normality and of homogeneity of variance underlie this test. More often than not, when these conditions are not met, Student’s t-test can be severely biased, and leads to invalid statistical inferences. Moreover, we argue that the assumption of equal variances will seldom hold in psychological research and that choosing between Student’s t-test or Welch’s t-test based on the outcomes of a test of the equality of variances often fails to provide an appropriate answer. We show that the Welch’s t-test provides a better control of Type 1 error rates when the assumption of homogeneity of variance is not met, and loses little robustness compared to Student’s t-test when the assumptions are met. We argue that Welch’s t-test should be used as a default strategy.

scholarly journals On the Statistical Testing Methods for Single Laboratory Validation of Qualitative Microbiological Assays with a Paired Design

2020 ◽  
Vol 103 (6) ◽  
pp. 1667-1679
Author(s):  
Shizhen S Wang
Keyword(s):  
Average Power ◽  
Mixed Effects ◽  
Error Rates ◽  
T Test ◽  
Type 1 Error ◽  
Minimum Detectable Difference ◽  
Microbiological Assays ◽  
Paired Design ◽  
Paired T Test

Abstract Background There are several statistical methods for detecting a difference of detection rates between alternative and reference qualitative microbiological assays in a single laboratory validation study with a paired design. Objective We compared performance of eight methods including McNemar’s test, sign test, Wilcoxon signed-rank test, paired t-test, and the regression methods based on conditional logistic (CLOGIT), mixed effects complementary log-log (MCLOGLOG), mixed effects logistic (MLOGIT) models, and a linear mixed effects model (LMM). Methods We first compared the minimum detectable difference in the proportion of detections between the alternative and reference detection methods among these statistical methods for a varied number of test portions. We then compared power and type 1 error rates of these methods using simulated data. Results The MCLOGLOG and MLOGIT models had the lowest minimum detectable difference, followed by the LMM and paired t-test. The MCLOGLOG and MLOGIT models had the highest average power but were anticonservative when correlation between the pairs of outcome values of the alternative and reference methods was high. The LMM and paired t-test had mostly the highest average power when the correlation was low and the second highest average power when the correlation was high. Type 1 error rates of these last two methods approached the nominal value of significance level when the number of test portions was moderately large (n > 20). Highlights The LMM and paired t-test are better choices than other competing methods, and we provide an example using real data.

Exact Type 1 Error Rates for Robustness of Student's t Test with Unequal Variances

1980 ◽  
Vol 5 (4) ◽  
pp. 337-349 ◽  
Author(s):  
Philip H. Ramsey
Keyword(s):  
Type I Error ◽  
Error Rates ◽  
T Test ◽  
Type I ◽  
Sample Sizes ◽  
Unequal Variances ◽  
Normal Populations ◽  
Type 1 Error ◽  
Student’S T ◽  
Equal Population

It is noted that disagreements have arisen in the literature about the robustness of the t test in normal populations with unequal variances. Hsu's procedure is applied to determine exact Type I error rates for t. Employing fairly liberal but objective standards for assessing robustness, it is shown that the t test is not always robust to the assumption of equal population variances even when sample sizes are equal. Several guidelines are suggested including the point that to apply t at α = .05 without regard for unequal variances would require equal sample sizes of at least 15 by one of the standards considered. In many cases, especially those with unequal N's, an alternative such as Welch's procedure is recommended.

scholarly journals Taking Parametric Assumptions Seriously Arguments for the Use of Welch’s F-test instead of the Classical F-test in One-way ANOVA (in press for the International Review of Social Psychology)

2018 ◽  
Author(s):  
Marie Delacre ◽  
Daniel Lakens ◽  
Youri Mora ◽  
Christophe Leys
Keyword(s):  
Statistical Power ◽  
Type I Error ◽  
Type I ◽  
International Review ◽  
F Test ◽  
Statistical Inferences ◽  
Student’S T ◽  
One Way Anova ◽  
Practical Recommendations ◽  
Student’S T Test

Student's t-test and classical F-test ANOVA rely on the assumptions that two or more samples are independent, and that independent and identically distributed residuals are normal and have equal variances between groups. We focus on the assumptions of normality and equality of variances, and argue that these assumptions are often unrealistic in the field of psychology. We underline the current lack of attention to these assumptions through an analysis of researchers' practices. Through Monte Carlo simulations we illustrate the consequences of performing the classic parametric F-test for ANOVA when the test assumptions are not met on the Type I error rate and statistical power. Under realistic deviations from the assumption of equal variances the classic F-test can yield severely biased results and lead to invalid statistical inferences. We examine two common alternatives to the F-test, namely the Welch's ANOVA (W-test) and the Brown-Forsythe test (F*-test). Our simulations show that under a range of realistic scenariosthe W-test is a better alternative and we therefore recommend using the W-test by default when comparing means. We provide a detailed example explaining how to perform the W-test in SPSS and R. We summarize our conclusions in practical recommendations that researchers can use to improve their statistical practices.

The Power of Student's t-Test

1965 ◽  
Vol 60 (309) ◽  
pp. 320 ◽  
Author(s):  
D. B. Owen
Keyword(s):  
T Test ◽  
Student’S T ◽  
Student’S T Test

scholarly journals Nurses' leadership styles in the icu: association with personal and professional profile and workload

2009 ◽  
Vol 17 (1) ◽  
pp. 28-33 ◽  
Author(s):  
Alexandre Pazetto Balsanelli ◽  
Isabel Cristina Kowal Olm Cunha ◽  
Iveth Yamaguchi Whitaker
Keyword(s):  
Leadership Styles ◽  
Leadership Style ◽  
T Test ◽  
Descriptive Statistics ◽  
Nursing Workload ◽  
Comparison Test ◽  
Multiple Comparison Test ◽  
Professional Profile ◽  
Student’S T ◽  
Student’S T Test

This study aims to explore the association between nurses' leadership styles and personal and professional nursing profile and workload. The sample consisted of seven nurses and seven nursing technicians who were grouped into pairs. At the end of three months, nurses were queried regarding what leadership style would be adopted when the nursing technician under their evaluation delivered care to patients admitted to the ICU. Relevant data was analyzed by applying descriptive statistics, Tukey's multiple comparison test and Student's t-test (p< 0.05). Nursing workload reached 80.1% on average. The personal and professional profile variables did not show any relation with the leadership styles chosen by nurses (p>0.05). The determine, persuade, and share leadership styles prevailed. However, whenever the nursing workload peaked, the determine and persuade styles were used (p<0.05).

scholarly journals Intravesical prostaglandin e2 effectiveness in the prevention of urinary retention after transvaginal reconstruction of the pubo-cervical fascia and short arm sling according to Lahodny: a prospective randomized clinical trial

2010 ◽  
Vol 14 (1) ◽  
pp. 15 ◽  
Author(s):  
G. QUADRI ◽  
N. NATALE ◽  
C. SPREAFICO ◽  
C. BELLONI ◽  
D. BARISANI ◽  
...  
Keyword(s):  
Prostaglandin E2 ◽  
Urinary Retention ◽  
Study Groups ◽  
T Test ◽  
Control Group ◽  
Fisher Exact Test ◽  
Test Results ◽  
Exact Test ◽  
Student’S T ◽  
Student’S T Test

Intravesical prostaglandin E2 is effective in the recovery of spontaneous voiding after transvaginal reconstruction of the pubocervical fascia and short arm sling according to Lahodny. The aim of the study was to compare the effects of intravesical prostaglandin E2 in the prevention of urinary retention after transvaginal reconstruction of the pubocervical fascia and short arm sling according to Lahodny. STUDY DESIGN: From November 1996 to June 1999 fifty women underwent the Lahodny procedure for moderate/severe cystocele and stress urinary incontinence. Women were randomly assigned to 1 of the 2 study groups: intravesical prostaglandin E2 versus controls. Data obtained were analyzed with the Student t test and the Fisher exact test. RESULTS: Two patients of the treatment group had to be excluded from the study, one because of the wrong measurement of the post-voidal residual volume and another due to a fastidious burning sensation which appeared immediately after prostaglandin instillation and required the suspension of the treatment. No other side effects such as nausea, vomiting, diarrhea or hyperthermia were observed. Patients who underwent the prostaglandin E2 treatment showed a recovery of spontaneous voiding after 7.9&plusmn;6.7 days, whereas this interval was significantly longer in the control group, being 12.9&plusmn;9.7 days (p=0.04, Two tailed Unpaired Student's T test). CONCLUSION: The effectiveness and the low associated morbidity mark the treatment with intravesical prostaglandin E2 useful in the recovery of normal voiding after transvaginal pubocervical fascia reconstruction and short arm sling with the procedure according to Lahodny.

scholarly journals Study of Relationship of Anemia among Edentulous Patients

2018 ◽  
Vol 5 (2) ◽  
pp. 105-108
Author(s):  
Lijo Isaac ◽  
A. P. Nirmal Raj ◽  
Reshma Karkera ◽  
R Naveen Reddy
Keyword(s):  
Nutritional Status ◽  
T Test ◽  
Dental Status ◽  
Adult Patients ◽  
Control Group ◽  
Age Group ◽  
Edentulous Patients ◽  
Student’S T ◽  
Relationship Of ◽  
Student’S T Test

Very little studies were done on relationship of the dental status and the nutritional status. The present study was done to study relation between edentulism and the presence of anemia. The study was included of 46 adult patients with edentulism and same numbers of patients were taken as controls. The results were tabulated and analyzed with the help of IBM SPSS statistics 20 using student’s t test. The hemoglobin levels were lower in the edentulous patients that that of the control group. The present study had shown that the nutritional status were poor resulting in anemia in case of edentulous patients as compared to control group with the same age group.  

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