Data and Measurements

Question 1

Independent variable

Answer 1

• what is being changed
• the proposed cause
• a predictor variable
• manipulated in experiments
• eg. drug A

Question 2

Dependent variable

Answer 2

• what is being measured
• the proposed effect
• the outcome
• eg. symptoms of disease B

Question 3

Co-variables

Answer 3

eg. time and money spent could be co-variables in an economic investigation

Question 4

Continuous Data

Answer 4

Interval variable:
- the difference between two values is meaningful
- the difference between 1 and 2 is equivalent to the difference between 99 and 100
Ratio variable:
- has all the properties of an interval variable and also has a clear definition of 0.0
- when the variable equals 0.0 there is none of that variable
- eg. height, weight, enzyme activity
- the ratios of scores on the scale must make sense
- not temperature or pH

Question 5

Categorical Data

Answer 5

Binary Variable:
- only two categories
- eg. dead or alive
Nominal Variable:
- more than two categories
- eg. omnivore, vegetarian, vegan, fruitarian
- for mutual exclusive but not ordered categories
Ordinal Variable:
- Pain indices, subjective assessments of “condition”; morphotypes
- the order matters but not the difference between values

Question 6

Quantitative Data

Answer 6

Measurable/objective measures on numeric value

Question 7

Qualitative Data

Answer 7

Pain indices; subjective assessments of “condition”; morphotypes

Question 8

Measurement Error

Answer 8

• the discrepancy between the actual value we’re trying to measure and the number we use to represent that value
• eg. you (in reality) weigh 80kg but the bathroom scales read 75kg
  80-75= 5 thus the measurement error is 5kg
• measurements without an understanding of uncertainty are meaningless! (error bars)

Question 9

Coefficient of variance

Answer 9

CV = standard deviation/mean * 100

Question 10

Indexed scatterplot

Answer 10

• a simple plot() of data points

- can be used to detect “runs”, or can be plotted in a sorted form

Question 11

Frequency distributions

Answer 11

• a.k.a. histograms
• a graph plotting values of observations on the horizontal axis, with a bar showing how many times each value occurred in the data set
• has an advanced technique known as density estimation that smooths out the internal binds to a continuous function

Question 12

Dotplot

Answer 12

A simple stacking of dots at each measure, analogous to a histogram

Question 13

Boxblot

Answer 13

• J. W. Tukey’s seminal 1969 revolution in date presentation that represents key features of a collection of measures
• the key properties are the display of the interquartile ranges, the mean and the median