L3

Question 1

What is a percentile

Answer 1

A way to verbally divide data into two parts at a key milestone. The percentile assigns the unit at the edge of the dividion . P percent of the population are lesser than the p’th percentile and 100%-p are greater. 25% are lesser than the 25th percentile and 75% are larger

Question 2

How do you calculate percentile

Answer 2

Order the data, index it and find the answer at the percentual equivalent of the percentile

Question 3

What measure of centrality is equal to the 50th percentile

Answer 3

The median

Question 4

What is the percentile if the dataset is not dividable by 100

Answer 4

Somewhere between the numbers available, different softwares give different answers

Question 5

What is the 90/10 quotient

Answer 5

A common measure of income inequality. Ratio between 90th and 10th percentile

Question 6

What is a decile

Answer 6

Division of data into ten equal parts D1 is 1-10 percentiles

Question 7

What is a quartile

Answer 7

Division of data into 4 equal parts Q1 is 1-25 percentile

Question 8

What is a quantile

Answer 8

A common name for all divisions of data along divisional lines such as percentiles, deciles and quartiles

Question 9

What is an abbreviation of the first quartile

Answer 9

Q1

Question 10

What is IQR

Answer 10

The inter quartile range is the middle 50% of values, the space between the 25th and 75th percentiles

Question 11

How do you draw a boxplot

Answer 11

Draw a box at the IQR and two wishers to the min and max values that are not further from the edges of the box than 1.5 IQR. Draw the median as a dashed line in the box and mark values outside the whiskers using an asterisk as outliers

Question 12

What does standard deviation tell us about a population

Answer 12

Only if observations tend to be close or far away from the mean

Question 13

What is chebyshevs theorem

Answer 13

That the proportion of observations that lie within k standard deviations of the mean is 1-1/k^2

Question 14

What is meant by the chebyshevs theorem being conservative

Answer 14

That it makes a conservative estimate meaning that it the proportion within k stdev can be higher than 1-1/k^2

Question 15

What is the empirical rule concerning standard deviation

Answer 15

That when distribution is normal (symmetrical and bell shaped) around 68% is within the first stdev and 95% are within the second while nearly all are within the third

Question 16

What is the z score of a variable

Answer 16

A standardized variable tells how many standard deviations away from mean a variable is. You subtract mean and divide by the standard deviation so that the standard deviation of z-score is always one

Question 17

How can you define an outlier in a population

Answer 17

If it is 1.5 IQR or 3 stdev away from mean

Question 18

What is covariance

Answer 18

The direction of the linear relationship between two variables. It is the k of the linear trend in a scaterplot

Question 19

What is the correlation coeficient

Answer 19

It tells the direction and strength of the linear relationship between two variables. It is unit free and always between 1 and -1.

Question 20

What does a correlation coefficient of -1 mean

Answer 20

Perfect negative relationship. All dots are in a perfect downward-sloping row in the scatterplot. Upward-sloping if positive

Question 21

What does a correlation coefficient of 0 mean

Answer 21

No correlation, no linear relationship

Question 22

When is correlation not causation

Answer 22

When changing one of two variables that tend to move together does not alter the other variable