Choosing Statistical Test 2 Flashcards
What is one sample t test used for?
To compare mean of single sample with known population mean to check if sample is derived from the population
What does one sample t test need?
Observed sample mean
Hypothesised derived population mean
What is needed for one sample t test?
Variable must be normally distributed
Sample size must be adequate to prevent extreme skewness
What is two sample t test also known as?
Students t
What is two sample t test used for?
To compare means of two samples
What does two sample t test need?
Two variables - one independent variable which can be nominal and a dependent variable which is quantitative
What does unpaired t test compare?
Independent samples where observation is made only once in each individual in a sample
What is compared in a paired t test?
Sample means are compared in same group
Here each subject is observed twice and scores are compared for statistical significance
What does t test assume?
Equal variance among two groups
What can be used to test variance between two groups?
Levenes test
What is ANOVA used for?
To compare means of multiple groups
What is ANOVA based on?
Variance comparisons
What is one-way ANOVA?
If one independent variable is compared across more than 2 groups
What happens in 2 way ANOVA?
2 independent variables are analyzed in multiple groups
When is repeated measures ANOVA used?
When same measures are used on multiple occassions
How is ANOVA calculated?
Using ratio of variation between groups to variation within groups
What is the name of the type of calculation used in ANOVA?
F statistics
Disadvantages of ANOVA
It can only tell us if a significant difference exists among groups; it does not tell us where the difference comes from
Why are post hoc significance tests used after ANOVA?
ANOVA cannot tell us where the difference came from
Assumptions made if ANOVA is used
Normal distribution of observations in groups
Equal variance among tested groups
Independent observations - not paired except for repeated measures test
Recommended test if >2 groups, 1 independent variable and testing between subjects
One way ANOVA
Recommended test if >2 groups, 1 independent variable and testing within subjects
Repeated measure ANOVA
Recommended test if >2 groups, >1 independent variable testing between subjects
Factorial ANOVA
Recommended test if >2 groups, >1 independent variable and testing within subjects
MANOVA
What is degrees of freedom (df)?
When we calculate an estimate of one statistic from an estimate of another
What happens to degree of freedom if applied to regression or ANOVA?
We lose one degree of freedom for each parameter estimate carried out before estimating the standard deviation
Degree of freedom for chi square if rows and columns marginal totals are specified
1
Degree of freedom if chi square distribution where proportions are estimated
(number of rows - 1) x (number of columns - 1)
What is the degree of freedom in a t test?
Sum of the persons in both groups minus 2
Degree of freedom in sample mean
n (sample size)
Df in population SD estimated from sample
n-1
Df in two sample t test
(n1 + n2) - 2
Df in chi square
(Rows - 1) x (columns - 1)
Df in one sample t
N - 1
Df in one way ANOVA: total variance
Total N - 1
Df in one way ANOVA within groups
Total N - number of groups
Df in one way ANOVA between groups
Number of groups - 1
