Introduction Statistics

Question 1

What is the mean?

Answer 1

• Average value
• Calculation: adding all values, dividing sum by
total numbers of observations
• Sensitive to outliers
Example: 1-3-3-4-9 • Sum=20
• Mean= 20/5= 4

Question 2

What is the median?

Answer 2

• Middle value
• Determining: ordering all values from small to
large and picking the middle
• Robust towards outliers
Example: 1-2-4-4-5
• Median: 4

Question 3

What is the mode?

Answer 3

• Highest frequency of value
• Determining: which value or category appears
most frequent.
• Robust towards outliers
Example: 1-2-2-4-12
• Mode: 2

Question 4

What is the interquartile range (IQR)?

Answer 4

• Used in boxplot (5-nr-summary)
• 1st Quartile: median of Min-M
• 3rd Quartile: median of M-Max Use:
• To identify possible outliers
• Calculation IQR: 𝑄3 − 𝑄1
• Outlier: larger than 1,5*IQR above/below 𝑄3 /
𝑄1

Question 5

What is a z-score? and when to use it?

Answer 5

• A standardized measure of standard deviations.
• Example: if SD=15 and a person has a score 15 points above the mean his Z-score= +1

• We can quickly determine how exceptional a given score is
• We can determine what percentage people will be within a range of two Z-scores, given that we
have a normal distribution