Lecture 11 9/18/24 Flashcards
How are data sets typically arranged?
-variables are in columns
-experimental units are in rows
What are the characteristics of nominal data?
-categories should be exhaustive
-categories should be mutually exclusive
-no comparative relationship is implied
What are the characteristics of ordinal data?
-categories should be all inclusive and mutually exclusive
-categories should have rank order with qualitative differences in relative amounts between the categories
-distances between categories are not assumed to be equal
What are the characteristics of continuous data?
-values should be all inclusive and mutually exclusive
-differences between values is uniform across the entire scale
What are the two types of continuous scale data?
-interval, measured in whole integers
-ratio, measured in decimals or fractions
Why is it important to distinguish between categorical and continuous variables?
-determines the method of presentation in graphs/tables
-determines the choice of statistical tests for significance
-different statistics are often used for nominal vs. ordinal variables
What are the characteristics of expressing continuous data as categorical?
-can always be done, but with a loss of information
-loss of information often leads to less statistical power
-continuous variables should only be categorized if there is good reason
When is it best to use mean vs. median to represent central tendency?
-mean works well in large populations with normal distribution
-median works well when the distribution is skewed
Which measures of central tendency are resistant to extreme values, and which are not?
resistant: median, mode
non-resistant: mean
Why is it important to NOT calculate a mean with number-labelled categories?
because they are categories, the difference between “numbers” does not need to be equal; therefore the mean does not actually represent the average of the population
What is measure of dispersion?
extent to which a set of scores deviate from some measure of central tendency for that set
What is range?
the difference between the largest and smallest values in the distribution
What do percentiles and quartiles measure?
the proportion of all observations that fall between specified values
What is kurtosis?
when the values in a data set skew either to the average of the data set or to the extremes of the data set
What is skewness?
when the values in a data set skew to one side of the data set (minimum or maximum)
