Counts and correlations

Question 1

Two types of difference

Answer 1

Differences in continuous variables among categories
Differences in frequencies of categorical events among categories

Question 2

Chi-Squared

Answer 2

We compare observed and expected frequencies and compute a statistic
Values of x^2 above a certain size correspond to p < 0.05

Question 3

Two situations in which we look for trends

Answer 3

When we want to know if two variables covary or correlate
May be casual relationship, but we don’t know what it is (May be result of shared cause)

Question 4

How do we test for casual relationships

Answer 4

Regression analysis

Question 5

Two correlation analysis tests

Answer 5

Pearsons correlation coefficient (parametric)
Spearman’s rank correlation (non-parametric)

Question 6

Assumptions of parametric correlation

Answer 6

Data are continuous
Data are normally distributed
Relationship between x and y is linear

Question 7

statistic r tells us:

Answer 7

r = 0
r = positive (0<r<q)
r = negative (-1<r<0)
r = +1 or -1