Descriptive Methods For Quantitative -2 Flashcards
Measure of center?
Mean, median, mode
Measure of spread / dispersion
Range, quartiles and standard deviation
Center: describe mean , median
Central location ( order numbers) of sample
Median : midpoint
Properties of mean and median
Mean is sensitive to skew and outliers
Median resistant to skews and outliers
50% of sample is above median and 50% of sample is below the median
Comparison of mean and median
Mean- used to summarize symmetric data vs median to summarize skewed data
Mean - sensitive to outliers and skew , median less sensitive to outliers and skew
Mean sum of all elements divided by n , median is the 50th percentile of the distribution
Mean - used together with SD to express variability, median used with IQR to express variability
Center : mode
Most frequently occurring value in the sample
Spread: range, variance ( and standard deviation)
Difference of largest and smallest observation
Spread : quartiles and percentiles
Quartiles are Q25: value at which 25% of the data are at or below the value
Q50: : 50% below and 50% above
Q75 : value at which 75% of data are at or below the value
Spread: Interquartile range (IQR)
Q25 : median of observation less than overall median
Q75 : median of observation to Brewster than overall median
IQR = Q75-Q25
When do we use standard deviation
To describe variations around the mean
Advantage of box plots
Clearly depicts symmetry and skewness
How to assess outliers using IQR
Low outlier: any value<(Q25-1.5IQR)
High outlier: any value > (Q75-1.5IQR)
Bivariate Plot and examples
Summarize relationships between 2 variables. Commonly used plots
1. Scatter plots - summary of relationship between 2 quantitive variables
2. Time plot - summary of relationship between time and quantitative variable
3. Box and whisker plots- summary of relationship of categorical variable and quantitative variable
What do time plots display
Overall trends
Cyclical patterns
