Chapter 19: Bivariate statistics

Question 1

Define bivariate data and explain why bivariate data needs to be studied

Answer 1

Bivariate data: data with 2 variables
- Studied to understand the relationship between the 2 variables

Question 2

Explain how association between the 2 variables can be observed

Answer 2

Using scatter plot (IV as x-axis, DV as y-axis)

1) Direction
- Upward trend: positive correlation (0>r>1)
- Downward trend: negative correlation (0<r<-1)
- Randomly scattered plots: no correlation

2) Linearity
- Linear trend
- Non-linear trend

3) Strength
- Strong 0.87<|r|<1
- Moderate: 0.7<|r|<0.87
- Weak: 0<|r|<0.7

4) Outlier

5) Causality
- Correlation does not indicate causality

Question 3

Explain how to draw line of best fit by eye

Answer 3

• Find mean point (x̄, ȳ) and ensure that line of best fit passes through mean point
• Ensure that the number of data points above and below the line of best fit are the same

Question 4

Apply the least squares regression line method to find the line that best fits the data

Answer 4

GDC: Spreadsheet –> Menu –> 4 –> 1 –> 3 (Linear regression)

y = ax+b

Question 5

Explain when to use regression of x against y (instead of y against x)

Answer 5

When y-variable is more accurate

x=my+b
y=1/m(x) +b

*GDC:
x-list: y variable
y-list: x variable