Lecture 5: Statistical testing Flashcards
The test to be used depends on?
The type of research question being asked and the design of the research
What are Descriptive studies?
Designed to explore prevalence
May not include any complex statistical test
The choice of the analysis depends on ?
the type of variables and levels of measurement used in the research
What are levels of measurement?
Nominal
Ordinal
Interval/ratio
What are Parametric tests?
Parametric tests make a number of assumptions about the distribution of the population from which the same is drawn ( e.g. normally distributed scores) and the nature of the data (interval or ratio level)
What are Non-parametric tests?
Non-parametric tests do not make assumptions about the distribution of the data and are often more suitable techniques for smaller samples or for when the data collected is measure on the ordinal or nominal level
What are two weaknesses of the non-parametric tests?
Less powerful - than parametric tests
Less likely to detect true differences or relationships that exist
Difficulty with interpretation - uses ranks rather than the raw value
Type of ParMetric tests?
Paired sample T-test
Independent T-test
1- way ANOVA
2- way ANOVA
Pearson’s correlation
Types of Non-parametric tests
Chi squared test
Wilcoxon signed- rank test
Mann-whitney U test
Kruskal- Wallis
Friedman
Spearman’s correlation
What is Correlation ?
Correlation is measure of strength and direction of the association between two variables
What is Pearson’s correlation?
Strength between two interval/ratio-level variables
What is Spearman rank correlation (Spearman’s rho)?
compares two ordinal-level variables
What is Point biserial?
correlation between categorical and continuous data
What is a correlation coefficient : r?
A correlation coefficient (r) is a way to put a value to the relationship.
r ranges from -1 to +1
What r (correlation coefficient)=0?
There is no relationship between the variables
Random scatter
What r (correlation coefficient)= -1?
Perfect negative correlation
What r (correlation coefficient)=+1?
Perfect positive correlation
What statistical test to use to compare means for 2 groups ?
Two-sample T test = Student’s T test
What statistical test to use to compare means for more than 2 Groups?
Analysis of variance= ANOVA
What Statistical test to use to compare means for 1 Group?
Paired T test
What Statistical test to use to compare proportions in a Big sample size?
Chi-square test
What Statistical test to use to compare proportions in a small sample size?
Fisher’s exact test
When do we use Independent sample t-test?
When we have two samples that are independent of each other and we want to compare the means of the two samples
•For example, you want to compare cholesterol levels between runners and swimmers.
When do you use Paired sample t-test
When we have two samples that are NOT independent of each other and we want to compare the means.
•For example, you want to know if a certain diet is effective at reducing LDL cholesterol levels (the bad kind of cholesterol). Could apply to pre- and post-data. E.g. mean cholesterol levels pre- and post- starting a diet plan
P value interpretation in Independent samples T-test
If the p-value < 0.05, there is a significant difference between the means of the two groups. Report the means of the two groups or the mean difference and confidence interval
P value interpretation in a paired samples- T test?
If the p-values <0.05 then there is a statistically significant difference between the two time points/experiments. Report the mean difference.
P value interpretation in Chi-squared test.
If p < 0.05, there is significant evidence that the proportions are not the same. Use %’s to describe what the relationship is.
Dependent and independent variables in Independent samples T-test?
Dependent variable: Continuous Independent variable: Categorical
Dependent and independent variables in Paired samples T-test?
Dependent variable: Continuous Time point: 1 or 2/ condition
Dependent and independent variables in Chi-square test?
Dependent variable: Categorical
Independent variable: Categorical
A study looks to determine the average cholesterol levels in smokers compared to non-smokers. Which statistical method should they use?
A Paired t Test B Two sample t test C Fishers exact test D Pearson’s Chi Squared E ANOVA F Spearman’s Correlation Coefficient
B
Researchers look to determine if there is a relationship between serum C reactive Protein levels and hormone replacement therapy.
Which is the best method to assess if HRT is related to CRP? A Paired t Test B Two Sample t Test C. Fisher’s Exact D. Chi-squared test
D
An obese population is given a new weight loss drug for a year to determine its efficacy. The patients are evaluated at baseline and then one year later. Which test should they use to determine if this drug is effective?
A Paired t Test B Two sample t test C Fishers exact test D Pearson’s Chi Squared E ANOVA F Spearman’s Correlation Coefficient
A
