Descriptive Statistics and Distributions

Question 1

biomedical data can be ___, ____, ____ or ____

Answer 1

biomedical data can be nominal, ordinal, interval or ratio

NOIR

Question 2

if the measure is constrained to be positive and the mean is _____, the measure must be right skewed

Answer 2

if the measure is constrained to be positive and the mean is less than ~2x the standard deviation, the measure must be right skewed

Question 3

describe application of the mean (average) and a con for using it

Answer 3

• most common measure of central tendency
• easy to model statistically; can be further averaged
• only for interval and ratio measures
• susceptible to extreme values

Question 4

describe application of the median (central)

Answer 4

• less affected by extreme values than the mean is
• harder to model statistically: cannot be averaged
• for ordinal, interval and ratio measures
• commonly used for skewed measurements:
  
  • biomarker measurements
  • income
• not susceptible to a few extreme values

Question 5

describe application of the mode (most common)

Answer 5

• not at all affected by extreme values
• for all types of data: most often used for nominal data
• can be misleading if there are many categories, or nonsensical for unrounded continuous variables
• very difficult to model statistically

Question 6

describe calculating the weighted mean

Answer 6

Question 7

pooling is only for the ____

Answer 7

pooling is only​ for the mean

Question 8

explain the different types of variability

Answer 8

• range: “total variability”
  
  • indicates extreme values
• interquartile range, IQR: “typical variability”
  
  • half of values fall within this range
  • not affected by a few extreme values
• variance: “typical squared variability”
  
  • easy to work with statistically
  • more affected by extreme values than IQR is

standard deviation: square root of variance

Question 9

describe the circumstances you would use the measures of variability

Answer 9

• use the range for any ordinal data
• use the interquartile range in the same settings you would use the median
• use the variance and SD in the same settings you would use the mean

Question 10

describe how to calculate range

Answer 10

Question 11

describe how to calculate the interquartile range

Answer 11