How to Conduct and Interpret Tests of Differences
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This document provides guidance on selecting and interpreting statistical tests for analyzing differences in variables using SPSS. It contrasts parametric and non-parametric techniques, offering specific examples for different scenarios like comparing two groups, multiple groups, and changes over time. Additionally, it highlights the importance of checking assumptions for each test and offers consulting services for dissertation support.
How to Conduct and Interpret Tests of Differences
- 1. How to Conduct and Interpret Tests of Differences Justin D’Souza Quantitative Specialist
- 2. Table of Contents Statistics Solutions Services Selecting an Appropriate Test SPSS Demo Summary Need help with your dissertation? Call 727-442-4290
- 3. Services Offered by Statistics Solutions • Topic Development • Prospectus or Concept Papers • Introduction Chapter • Literature Review Chapter (identifying articles) • Methodology Chapter (Quantitative/Qualitative). • IRB forms • Data entry templates • Survey Monkey upload • Results Chapter (Quantitative/Qualitative) • Discussion Chapter • Powerpoints for Defense • Journal Publications Need help with your dissertation? Call 727-442-4290
- 4. Parametric and Non-Parametric Statistics Parametric Techniques Parametric statistics are based on assumptions about the distribution of population from which the sample was taken. Usually this “assumption” is that the data follows a normal (bell-shaped) distribution. Non-Parametric Techniques Nonparametric statistics are not based on assumptions, that is, the data can be collected from a sample that does not follow a specific distribution. A normal (bell-shaped) distribution is not required for non-parametric techniques. Need help with your dissertation? Call 727-442-4290
- 5. Normality Assumption Normality Assumption Typically, parametric statistics assume that the data follow a normal (bell-shaped) distribution. There are various ways to check for normality (Shapiro-Wilk test, Kolmogorov- Smirnov test, skewness/kurtosis, scatterplots/histograms). And if the data do not follow a normal distribution, non-parametric techniques can potentially be used as an alternative. If you have a large sample size (>50), you can use the central limit theorem to justify using parametric techniques even if tests normality are not showing a bell- shaped curve. Howell (2013) states that violations of normality are not problematic when the sample size for research exceeds 50 cases. Need help with your dissertation? Call 727-442-4290
- 6. Differences in Variable Between Two Groups
- 7. Differences in Variable Between Two Groups Sample Research Question: Is there a significant difference in math scores between males and females? Parametric Technique Independent sample t-test – Appropriate statistical analysis when testing for differences in a continuous (interval/ratio) variable between two groups. Non-Parametric Technique Mann-Whitney U test– Appropriate statistical analysis when testing for differences in an ordinal variable (or non-normal continuous variable) between two groups. Need help with your dissertation? Call 727-442-4290
- 8. Setting Up Independent Sample t-test and Mann-Whitney U Test Need to have an independent variable that is dichotomous (two groups). Examples: Gender (male vs female), group in experimental study (treatment vs control) Need to have a continuous or ordinal dependent variable. Check for assumptions of an independent sample t-test or Mann-Whitney U test. https://statistics.laerd.com/spss-tutorials/independent-t-test-using-spss- statistics.php https://statistics.laerd.com/spss-tutorials/mann-whitney-u-test-using-spss- statistics.php Run your statistical analysis in SPSS. Need help with your dissertation? Call 727-442-4290
- 9. Differences in Variables Between Two or More Groups
- 10. Differences In Variables Between Two or More Groups Sample Research Questions: Is there a significant difference in math scores between classes (Class 1, Class 2, and Class 3)? Is there a significant difference in math scores and science scores between classes (Class 1, Class 2, and Class 3)? Parametric Technique Analysis of Variance (ANOVA)– Appropriate statistical analysis when testing for differences in one continuous (interval/ratio) variable between two or more groups. Multivariate Analysis of Variance (MANOVA)– Appropriate statistical analysis when testing for differences in multiple continuous (interval/ratio) variables between two or more groups. Non-Parametric Technique Kruskal-Wallis Test– Appropriate statistical analysis when testing for differences in an ordinal variable (or non-normal continuous variable) between two or more groups. There is not a non-parametric alternative to running multiple dependent variables at once. Instead run a single Kruskal-Wallis Test for each dependent variable.
- 11. Setting Up ANOVA, MANOVA, and Kruskal-Wallis Test Need to have one or more independent grouping variables with two or more groups. Examples: Ethnicity, Grade Level, College Major Need to have one or more continuous or ordinal dependent variables. Check for assumptions of an ANOVA, MANOVA, or Kruskal-Wallis test. https://statistics.laerd.com/spss-tutorials/one-way-anova-using-spss- statistics.php https://statistics.laerd.com/spss-tutorials/one-way-manova-using-spss- statistics.php https://statistics.laerd.com/spss-tutorials/kruskal-wallis-h-test-using-spss- statistics.php Run your statistical analysis in SPSS. Need help with your dissertation? Call 727-442-4290
- 12. Differences in Variable Between Two Points in Time (Pretest vs Posttest)
- 13. Differences in Variable Between Two Points in Time (Pretest vs Posttest) Sample Research Question: Is there a significant difference in reading test scores between pretest and posttest? Parametric Technique Dependent (paired) sample t-test – Appropriate statistical analysis when testing for differences in a continuous (interval/ratio) variable between two points in time. Non-Parametric Technique Wilcoxon-Signed Rank test– Appropriate statistical analysis when testing for differences in an ordinal variable (or non-normal continuous variable) between two points in time. Need help with your dissertation? Call 727-442-4290
- 14. Setting Up Dependent Sample t-test and Wilcoxon-Signed Rank Test Need to have one dependent variable that is measured two times. Check for assumptions of a dependent sample t-test or Wilcoxon- Signed Rank test: https://statistics.laerd.com/spss-tutorials/dependent-t-test-using- spss-statistics.php https://statistics.laerd.com/spss-tutorials/wilcoxon-signed-rank- test-using-spss-statistics.php Run your statistical analysis in SPSS. Need help with your dissertation? Call 727-442-4290
- 15. Differences in Variable Between Three or More Points in Time (T1 vs T2 vs T3….)
- 16. Differences in Variable Between Three or More Points in Time (T1 vs T2 vs T3…) Sample Research Question: Is there a significant difference in reading test scores between pretest, midterm, posttest, and follow-up? Parametric Technique Repeated Measures ANOVA – Appropriate statistical analysis when testing for differences in a continuous (interval/ratio) variable between three or more points in time. Non-Parametric Technique Friedman ANOVA– Appropriate statistical analysis when testing for differences in an ordinal variable (or non-normal continuous variable) between three or more points in time. Need help with your dissertation? Call 727-442-4290
- 17. Setting Up Repeated Measures ANOVAand Friedman ANOVA Need to have one dependent variable that is measured three or more times. Check for assumptions of a repeated measures ANOVA or a Friedman ANOVA: https://statistics.laerd.com/statistical-guides/repeated-measures-anova- statistical-guide.php https://statistics.laerd.com/spss-tutorials/friedman-test-using-spss- statistics.php Run your statistical analysis in SPSS. Need help with your dissertation? Call 727-442-4290
- 18. Differences in Variable Between GroupsAND Time
- 19. Differences in Variable Between GroupsAND Time Sample Research Question: Is there a significant difference in reading test scores by class and pretest/posttest? Parametric Technique Mixed Model ANOVA – Appropriate statistical analysis when testing for differences in multiple continuous (interval/ratio) variables between groups AND time. Non-Parametric Technique There is not a non-parametric technique for simultaneously examining for differences in groups and time. Need help with your dissertation? Call 727-442-4290
- 20. Setting Up Mixed Model ANOVA Need an independent grouping variable (such as treatment vs control). Need to have one continuous dependent variable that is measured two or more times. Check for assumptions of a mixed model ANOVA: https://statistics.laerd.com/spss-tutorials/mixed-anova-using-spss- statistics.php Run your statistical analysis in SPSS. Need help with your dissertation? Call 727-442-4290
- 21. Summary Determine what level of measurement of variables you are using. Identify all independent and dependent variables. Is goal to test for differences between groups, test for differences over time (intervention), or both? Use SPSS to check for assumptions, analyze your data, and present interpretations. Need help with your dissertation? Call 727-442-4290
- 22. Additional Support Statistics Solutions is a full-service dissertation consulting company providing graduate students timely, editorial support for their dissertations and scholarly projects For information about our services, receive a complementary 30-min consultation available Mon-Fri 9-5 ET Contact us at info@statisticssolutions.com Phone: 727-442-4290