Intro to data science (wk 2)

Question 1

What is a population?

Answer 1

A complete subset of objects e.g. all UG students

Question 2

What is a sample?

Answer 2

A subset of a given population e.g. a group of students in this module out of all UG students

Question 3

What is a variable?

Answer 3

A variable is a set of related events that can take in more than one value

Question 4

What is an independent variable?

Answer 4

-The IV is the variable representing the value being changed or manipulated.
-It’s controlled or selected to determine its relationship on an observed outcome

Question 5

What is a dependent variable?

Answer 5

-The DV is the observed result of the IV being manipulated.
-It is something that (may) depend on the IV

Question 6

Levels of IVs

Answer 6

-An IV can be composed of different categories
-These are called levels, conditions or treatments
-This is different from the number of IVs- you only belong to one level, but have multiple IVs

Question 7

What is a control variable?

Answer 7

-Variables that are kept constant to prevent them influencing the effect of IV on DV
-Critical for study design (e.g. recruitment criteria for participants)

Question 8

What is nominal data (categorical)?

Answer 8

-Cannot be ordered, cannot be counted e.g. country, gender, occupation

Question 9

What is ordinal data?

Answer 9

-Can be ordered, but cannot be added or subtracted e.g. satisfaction rating, education level

Question 10

What is interval data?

Answer 10

-Can be ordered, and their difference can be measured, but you cannot compute a ratio between two value (no meaningful zero exists) e.g. exam date

Question 11

What is ratio data?

Answer 11

-Interval and can take ratio between two (has a meaningful zero) e.g. distance, height, annual income

Question 12

What 2 data sets are qualitative and categorical

Answer 12

Nominal and ordinal values

Question 13

What 2 data sets are quantitative and continuous

Answer 13

Interval and ratio

Question 14

What is a histogram?

Answer 14

Histograms visualises how data is distributed

Question 15

What are the 3 central tendencies?

Answer 15

Mode, median, mean

Question 16

What is the mode?

Answer 16

-There can be multiple modes
-Can be used for all types of variables, and often used for nominal and ordinal variables

Question 17

What is the median?

Answer 17

-Median cannot be obtained for nominal variables, it can be obtained only on ordered variables (i.e. ordinal, interval and ratio)

Question 18

What is the mean?

Answer 18

Mean can only be defined in interval and ratio variables

Question 19

What is the 2nd moment?

Question 20

What is the 3rd moment/ skewness

Answer 20

-Skewness is another parameter informing the shape of distribution, other than mean and variance
-Zero skewness means data are symmetrically distributed
-High skewness means distribution is highly asymmetrical
-Positive/negative skewness indicates which direction data are skewed

Question 21

What is the 4th moment?

Question 22

What is kurtosis?

Answer 22

-Kurtosis means the sharpness
-Always positive by definition but normally be subtract 3 - this is called the excess kurtosis
-Kurtosis -> how thin

Question 23

What are the 2 popular methods to detect outliers?

Answer 23

1. Based on z-score -> outlier is more than 3 or less than -3
2. Based on IQR (inter-quartile range) -> width between the 1st and 3rd quartile. Is an outlier of the value is greater than 1.5 IQR above the 3rd quartile, or smaller than 1.5 IQR below the 2nd quartile.

Question 24

What is a box plot?

Answer 24

-Box plot is a plot summarising quartile-based statistics of a data set
-A box plot includes:
1. Location of quartiles
2. Range of data excluding outliers
3. Outliers detected by quartile