03. Review of Basic Data Analytic Methods Using R

Question 1

What is a factor

Answer 1

A factor is vector of values that are limited to a fixed set of values (categories). Factors always have levels (the things it allows to be put in - like it had a data validation drop down list). When you first create the factor it will assume the different options are the initial options, after that it will check against this set of levels.

Question 2

What is a list

Answer 2

A list is a vector of values which can contain different data types

Question 3

What is an array

Answer 3

An array can only contain the same type of data. Arrays can multi-dimensional. i.e. rows and columns and sheets and workbooks etc

Question 4

What is a dataframe

Answer 4

A dataframe is a table of vectors or factors; all items of the same length. Individual columns are the same data type, but different columns can be different data types.

Question 5

What is a record

Answer 5

A single cell

Question 6

What is a pairs plot

Answer 6

It plots every variable against every other variable. Also known as a Splom or a ScatterPlot

Question 7

What do T-Tests use

Answer 7

Samples of the population (not the full population)

Question 8

What are T-Tests use

Answer 8

Samples of the population (not the full population) are tested to compare against a NULL hypothesis (i.e. checking if there is a statistical significance)

Question 9

What can an AVOVA test be used for

Answer 9

AVOVA are used in hypothesis testing when you have more than two sample populations

Question 10

What is hypothesis testing

Answer 10

where you are picking between the null and the alternative hypothesis

Question 11

What is statistical power

Answer 11

Statistical Power is a measure of how well that test compares against the null

Question 12

What is a parametric distribution

Answer 12

The data follows a normal distribution

Question 13

How is the standard deviation calculated

Answer 13

The standard deviation is the square root of the deviance

Question 14

The T-Test

Answer 14

Parametric. Can be one test and two test

A “students t-test” is another name for the two sample t test.

Question 15

Welch’s test

Answer 15

Parametric. But can cope with different standard deviations (hence automatically two sample)

Question 16

Wilcoxon Rank Sum Test

Answer 16

Non-Parametric. It tests is two populations of numbers are equally distributed.

Question 17

AVOVA

Answer 17

We use ANOVA tests to perform multiple comparisons across more than two populations of data.
Example: You have an online shop that gives two offers or none at all. We want to find out whether the offers are affecting the number of purchases.
The point of the ANOVA is to determine whether the variance in the dataset is due to the spread of values within each group or because of the spread of values between groups.

Question 18

What is the p value

Answer 18

The P-value is the likelihood that the NULL hypothesis is true. So a low p value means the NULL is very unlikely so happy days.

Question 19

What is a vector

Answer 19

A vector can only consist of one class and represents a single column

Question 20

What is a matrix

Answer 20

A two dimensional array

Question 21

If we reject the NULL hypothesis but it is actually true what type of error is this

Answer 21

Type 1 error

Question 22

How does the AVOVA test work

Answer 22

It’s like clustering and looks at the between groups mean sum of squares (between group variance) and the within group mean sum of squares (within group variance)