Descriptive Analytics

Question 1

Data

Answer 1

Set of pieces of individual information (can be likes, tweets, etc.)

Question 2

3 Question to Ask With New Data

Answer 2

1) How many variables in dataset?
2) How many observations in the dataset?
3) What level are the observations (customer, transaction, store, etc.)?

Question 3

Quantitative

Answer 3

Scale relevant
Numerical

Question 4

Qualitative

Answer 4

Set of categories

gender {m,f,o} being {0,1,2} doesn’t mean o is double the value of f

Question 5

Discrete

Answer 5

Takes only certain values

Question 6

Continuous

Answer 6

Can take on any numerical value

Question 7

Variation

Answer 7

Observations for one variable will take on different values, not all values for “churn” will be the same in the data set

Question 8

Mean

Answer 8

Average

Sensitive to outliers

Question 9

Median

Answer 9

Middle most value

Ignores a lot of information
Can move abruptly

Question 10

Mode

Answer 10

Most common value

Not good for continuous variables

Question 11

Frequency Distribution

Answer 11

Table showing fraction of observations for which a variable takes on each possible value

Variable. # Obs. % of overall Obs
A
B
C

Question 12

Range of Values

Answer 12

Important if you care about the likelihood of a good outcome - blockbuster

Want to avoid a bad- healthcare

Care about inequality/dispersion- inventory management

Question 13

Interquartile Range

Answer 13

Difference between 25th and 75th percentile

Question 14

Standard Deviation

Answer 14

sqrt(variance)

gives the average variation around the mean in the units of the variable

lower means data close to the mean

higher means data spread out

Question 15

Coefficient of Variation

Answer 15

SD/Mean

Compares degree of variation between data sets

Question 16

Summary Statistics

Answer 16

On numerical variables #obs, mean, median, std dev, min, max

Question 17

Data will have

Answer 17

Randomness
Measurement Error
True Unexplained Factors (things we didn’t realize impacted our variable of interest

Question 18

Data will have

Answer 18

Randomness
Measurement Error
True Unexplained Factors (things we didn’t realize impacted our variable of interest

Question 19

Tools to Uncover Systematic Relationships

Answer 19

Scatter Plot
Binned Scatter Plot
Coefficient of Correlation
Conditional Means
Cross Tab

Question 20

Binned Scatter Plot

Answer 20

Reduce data points by taking conditional means of y values

Question 21

Coefficient of Correlation

Answer 21

Measures direction and strength on linear relationship between quant variables

Sign = direction
Abs Val = strength
Always between -1 and 1, unit less, not slope
X with Y = Y with C

V shape will make 0 because it cancels out

Question 22

Conditional Means

Answer 22

Mean of different x values on different y values to show relationship
Must be numerical
Best if y is discrete or has categories
Can be y vs a dummy variable x

Question 23

Cross Tab

Answer 23

Measures the frequency that certain combinations of features occur using conditional means

Ie Airports on rows and Buckets of Delays on Columns

Question 24

Confounding Effects

Answer 24

Mixture of Effects

Question 25

Descriptive Analysis Steps

Answer 25

1) Get to know data
2) Explore distribution
3) Explore correlations between key variables
4) Recognize some variation is driven factors- we don’t know or can’t measure