Module 3

Question 1

What is a variable?

Answer 1

any measureable characteristic of an observation unit (ex. the number of facebook posts that a person might read each day). can vary among sampling units

Question 2

What is the 3 pieces of information a variable contains?

Answer 2

• what the variable repersents
• the measurement unit
• description of observation unit

Question 3

What is the datum/data?

Answer 3

the value of a variable that you measure from an observation unit

Question 4

Difference between numerical and categorical variables?

Answer 4

numerical: the data is numeric (have measurement units that indicate the scale)

categorial: the data is a qualitative description (have no measurement units)

Question 5

What is a continuous numerical variable?

Answer 5

• can take on continuous numers (any number, even fractional numbers)

Question 6

What is a discrete numerical variable?

Answer 6

can only take on whole numbers (integers)

Question 7

What is an ordinal categorical variable?

Answer 7

can take on qualitative values but where the values are from a ranked scale (ex. using a scale to describe how you’re feeling)

Question 8

What is a nominal caregorical variable?

Answer 8

can take on qualitative values but where the values do not have a particular order (ex. food)

Question 9

How is categorical data characterized

Answer 9

• counts: the number of sampling units in each category
• proportions: the share of the total sampling units in each category

Question 10

Which is easier to undersand when doing descriptive statistics: counts or proportions

Answer 10

proportions

Question 11

What do counts and proportions indciate?

Answer 11

the central tendency of categorical data

Question 12

what is range? and what is it used to indicate?

Answer 12

• range is used to indicate dispersion
• describes the variation in the esponse variable

Question 13

What are the two approachs used to determine descriptive statistics for numerical variables?

Answer 13

• means
• quartiles

Question 14

What does the mean characterize?

Answer 14

the central tendency of a numeric variable

Question 15

What is variance and how is it calculated?

Answer 15

• measure of amount of variation in sample
• calculated as average squared distance of each data point from sample mean (all summed) then divided by number of data points

Question 16

What is standard deviation?

Answer 16

• square root of variance
  *

Question 17

What are quartiles?

Answer 17

• are specific values of the variable that divide your data into ranked groups
  *

Question 18

What is the central tendency given by?

Answer 18

the second quartiles, is also called the median (50% above and 50% below)

Question 19

What is the interquartile range?

Answer 19

uses quartiles to describe dispersion in a numerical variable. It is the difference between the 3rd and 1st quartiles and gives the range of the innermost 50% of a numerical sample.

subtract 1st quartile from 3rd

Question 20

What are the pros of using quartiles?

Answer 20

• median and interquartile range are relatively robust to extreme values (not as affected by the extremes)

Question 21

cons of using quartiles?

Answer 21

the median and interquartile range can become variable for samples with small number of observations (more sensitive)

Question 22

Pros of using means?

Answer 22

mean and standard deviation are more robust when small number of observations

Question 23

cons of using means?

Answer 23

downside of mean and standard deviation is that they are sensitive to extreme values

Question 24

When is it better to use quartiles?

Answer 24

when characterizing numerical values, as long as the number of observations is not too small

Question 25

What is effect size?

Answer 25

the change in mean value of the response variable among groups. allows us to evaluate whether the change in the response variable is meaningful for a particular study

Question 26

What is effect size calculated among?

Answer 26

between treatment levels (one possibility)