Lecture 11 - Issues involving spatial data

Question 1

Spatial autocorrelation

Answer 1

• main issue in spatial analysis
• statistically prove that things are related in space (clustering / dispersion)
• be careful if finding two things are correlated (move in the same or opposite directions) but aren’t actually variables that are related (example: people drowning and divorces in Kentucky)

Question 2

Modifiable Areal Unit Problem

Answer 2

• same data with different results when aggregated differently
• affects correlation & regression
• applies where data aggregated at different areal units
• in NZ - territorial authorities, areal units, meshblocks
• typically larger areas better model, smaller areas lower model performance

Question 3

MAUP - Scale effects

Answer 3

Analytical differences depending on size of units used (correlations are more pronounced for bigger units)

Question 4

MAUP - Zonation effects

Answer 4

Major differences depending on how study are is divided up, even at the same scale
Can result in change to strength and nature of relationship.

Question 5

Gerrymandering

Answer 5

• example of MAUP
• political manipulation of map boundaries so that citizens divided up into districts limiting ability to represent themselves via voting

Question 6

Ecological Fallacy

Answer 6

-inferences about the nature of individuals deduced from inferences about the group those individuals belong to

• might observe a strong relationship between income and crime at the areal unit level, with lower-income associated with higher crime rates
• our (not correct) conclusion?
  1. lower-income persons more likely to commit a crime
  2. lower-income areas associated with higher crime
  3. higher-income areas tend to experience lower crime rates

-one variable at individual level and one at group level

Question 7

Ecological Correlation Problem

Answer 7

-correlation between 2 variables at the group level, in contrast to correlations between 2 variables at the individual level

-example: correlation between per capita alcohol consumption and death rates of males 55-64
and
number of drinks per day compared against mortality rates per 1,000 people

-people who drank modestly had lower mortality rates than those who didn’t drink at all, but among higher levels of individual consumption there was a striking linear increase in mortality

Question 8

Ecological Fallacy Solutions

Answer 8

• limit inferences from ecological studies to determinates of aggregate population health
• if ecological study design is used to investigate determinates of individual health:
• choose homogeneous (small) units
• control for determinates of background risk
• be aware of limitations of causal inference

Question 9

Nonuniformity of space/edge effect problems

Answer 9

• space is not uniform
• gaps and clusters no unexpected but arise resulting from the non-uniformity of urban space (might have higher crime just because there’s more population there, low crime because its a water body)
• artificial boundaries are imposed on a study area (often just) to keep it manageable
• something might be explained by something happening just outside the study area (people move across artificial boundaries)

Question 10

Spatial Questions

Answer 10

1. What I need to find out?
2. Who’s my audience?
3. Define hypothesis to be tested
4. What do I already know about the spatial patterning of data that will help in exploring the problem?
5. Where is the phenomenon coming from? (regression)
6. What local initiatives have been targeted in past to area of interest? (things that could be the cause of changes over time)
7. What spatial data do I need?
8. What are the limits of data used in spatial analysis? (accuracy)