Descriptive stats: measures of dispersion

Question 1

what is variance?

Answer 1

average squared differences of scores from the mean

Question 2

what is standard deviation?

Answer 2

square root of the variance

• small standard deviation = values are close to the mean
• large standard deviation = values are far from the mean

Question 3

what is the range?

Answer 3

difference between the largest and smallest value

Question 4

what is the interquartile range?

Answer 4

difference between the 75th and 25th percentile of our data

Question 5

what is the issue with the range?

Answer 5

outliers affect value significantly

Question 6

how do you calculate IQR?

Answer 6

1) calculate median (Q2)
2) calculate median of lower half (Q2) and upper half (Q3)
3) IQR is difference between Q1 and Q3

Question 7

what is normal distribution

Answer 7

symmetric distribution with no skew on either side

bell shaped

Question 8

what is standard normal distribution?

Answer 8

normal distribution with a mean of 0 and a SD of 1

we can use this to see how extreme our values are, and to compare date which may be in different units

68% of all data lies within one SD of the mean
95% lies within two SDs
99.7% lies within three SDs

Question 9

what are Z scores?

Answer 9

number of CDs away from the mean