Module 4

Question 1

w

what is a contingency table?

Answer 1

data frequencies or proportions within different levels of categorical variable.

Question 2

What are one way and two way contingency tables?

Answer 2

• they jusr refer to the number of categorical variables you observe for each sampling unit

Question 3

What are marginal dsitributions?

Answer 3

• one way to see overall patterns in the data
• claculate row and column frequencies
• the row and column sums of a two-way contingency table. They can be shown as frequencies or proportions.

Question 4

How to find marginal distributions in rows vs columns?

Answer 4

rows: sum frequencies accross all columns for each row

column: sum frequencies accross all rows for each column

Question 5

what are conditional distributions?

Answer 5

two-way tables that show the proportion of sampling units for one variable within each level of the second variable. the interaction between categorical variables (shown as seperate table)

Question 6

How create conditional distribution?

Answer 6

select one of the categorical variables to be the primary variable and the other one to be the secondary (conditional) variable

Question 7

How are conditional distributions calculated?

Answer 7

calculated as the frequency from contingency table divided by the marginal distribution of the primary variable

• identify primary and secondary variable
• for each cell in the new table, divide the value from the contingency table by the marginal distribution of the primary variable

Question 8

What do contiditonal distributions show us in regards to the variables?

Answer 8

allow us to see how the secondary variable changes accross the primary variable

Question 9

What is a bar graph?

Answer 9

used to visualize categorical data

vertical or horizontal orientation

Question 10

What are two variable bar graphs?

Answer 10

• can be used to display data with two categotical measurement variables
• designate one variable as the grouping vairable (forms the base of the figure, and levels of the other variable are shown within each level)
• next step: do we create it as a grouped bar chart or a stacked bar chart?

Question 11

What type of variable is good for a grouping variable?

Answer 11

ordinal categorical variables

Question 12

What are grouped bar charts

Answer 12

• the second variables are shown beside each other within each level of the grouping variable
• levels of grouping variable are separated using a large gap

Question 13

What is a stacked bar chart?

Answer 13

• levels of the second variable are stacked on top of one another within each level of the grouping variable
• just one bar for each level of the grouping variable (color used to sepearate)

Question 14

What are histograms?

Answer 14

• visualize numerical data
• split numerical data into bins of equal size and display the number of sampling units in each bin

Question 15

what are the three steps of how histograms are created?

Answer 15

• divide the numerical variable into a number of bins of equal size
• count how many sampling units fit within each bin (frequency)
• create a plot where each bin has abar with a height equal to the frequency of that bin, make sure no gaps between the bars

Question 16

Advantages of histograms?

Answer 16

• good way to visualize pattern of relative abundance in your sampling units along the numerical variable

Question 17

Disadvantage of histogram?

Answer 17

complicated to display hisograms when the dataset has many levels of categorical variable

Question 18

what is a bin?

Answer 18

a small range of the numerical variable. The numerical variable is divided into a number of bins of equal size forming the base of the figure.

Question 19

What are box plots?

Answer 19

• visualize numerical data
• based on quartiles and are popular because they show five descriptive statistics in relative compact design

Question 20

What do boxplots show?

Answer 20

• 1st quartile
• 3rd quartile
• minimum
• median
• maximum

Question 21

What happens with grouped box plots for categorical groups?

Answer 21

• designate one categorical variable as the grouping variable
• the second as the secondary variable
• grouping variable forms the base of the figure
• the levels of the secondary variable are shown within each level of the grouping variable

Question 22

When should we use histograms vs box plots

Answer 22

if you have numerical data for a small number of categorical groups and want to showcase the shape of the data distribution, then histograms are the choice.

if you have many categorical groups, or are not interested in showcasing the shape of the data distribution, then use box plot

Question 23

What is a scatter plot?

Answer 23

• used to visualize the relationship between two numerical variables
• each point on the scatterplot is a sampling unit
• both numerical variables are measured from the same sampling unuit

Question 24

What is the independent vs dependent variable?

Answer 24

independent: the experimental treatment that is manipulated

dependent: the measured response under those treatments

Question 25

What are line plots?

Answer 25

used when you have data on two numerical variables, and where the researcher has taken repeated measures from the same sampling unit

the repeated measurements for each sampling unit are connected together by a line so that the viewer knows the data points are not independent of each other