Chapter 17 Testing Simple Causal Models

1
Chapter 17Testing Simple Causal Models

• Angela Gillis Winston Jackson
• Nursing Research Methods Interpretation

2
Testing Causal Models

• In non-experimental research the demonstration of
  causality is more difficult than in experimental
  research.
• To establish causality you must show that
• variables are associated
• plausible causal sequence
• variables not spuriously connected

3
Testing for an Intervening Variable

• Parental
• Health Value
• X

Healthful Lifestyle Choices Y
Parental Pressure I
4
The Rationale...

• If the model is correct, X should only be able to
  influence Y through the intervening variable.
• If we hold the I variable constant X cannot
  influence Y

5
Jacksons Rule of Thirds...

• We compare the original difference to what
  happens to the difference when we run the
  control, if the new difference
• increases by 1/3 or more increased
• ? 1/3 stay same
• - 1/3 or more decreased/disappeared
• difference across categories mixed

6
Using Crosstabs...

• Original Difference
• Low Health Value High Health
• healthy choices 73.1 88.9
• Difference 15.8

7
Calculating the Thirds

• Difference 15.8 (88.9 - 73.1)
• Third 15.8 / 3 5.3
• Increased if gt 15.8 5.3 gt 21.1
• Stayed Same if 15.8 5.3 10.5 - 21.1
• Decreased if lt 10.5
• Mixed if Different in two categories

8
Crosstabs Outcome 1

• Original Difference
• Low Health Value High Health Value
• healthy lifestyle choices 73.1
  88.9
• Difference
  15.8
• Outcome 1
• Friends Healthy Choices
  Friends Unhealthy Choices
• Parents Health Value Low High
  Low High
• Healthy Choices 92.0 93.0
  71.0 69.0
• Difference
  1.0 -2.0

9
Crosstabs Outcome 2

• Original Difference
• Low Health Value High Health Value
• healthy lifestyle choices 73.1
  88.9
• Difference
  15.8
• Outcome 2
• Friends Healthy
  Choices Friends Unhealthy Choices
• Parents Health Value Low High
  Low High
• Healthy Choices 74.0 92.0
  71.0 86.0
• Difference
  18.0 15.0

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Crosstabs Outcome 3

• Original Difference
• Low Health Value High Health Value
• healthy lifestyle choices 73.1
  88.9
• Difference
  15.8
• Outcome 3
• Friends
  Healthy Choices Friends Unhealthy Choices
• Parents Health Value Low High
  Low High
• Healthy Choices 85.0 92.0
  68.0 76.0
• Difference
  7.0 8.0

11
Crosstabs Outcome 4

• Original Difference
• Low Health Value High Health Value
• healthy lifestyle choices 73.1
  88.9
• Difference
  15.8
• Outcome 4
• Friends
  Healthy Choices Friends Unhealthy Choices
• Parents Health Value Low High
  Low High
• Healthy Choices 74.0 96.0
  61.0 82.0
• Difference
  22.0 21.0

12
Crosstabs Outcome 5

• Original Difference
• Low Health Value High Health Value
• healthy lifestyle choices 73.1
  88.9
• Difference
  15.8
• Outcome 5
• Friends Healthy
  Choices Friends Unhealthy Choices
• Parents Health Value Low High
  Low High
• Healthy Choices 90.0 92.0
  60.0 82.0
• Difference
  2.0 22.0

13
Using Means in Test...

• Original Difference
• Low Parental Health Value
  High Parental Health Value
• Healthy Lifestyle Choices 24.7
  38.7
• Difference
  14.0
• Thirds 14.0 / 3 4.7
• Increased if gt 14.0 4.7 gt18.7
• Stayed Same if 14.0 4.7 9.3 - 18.7
• Decreased if lt 9.3
• Mixed if Different in two categories

14
MeansOutcome 1

• Original Difference
• Low Parental Health Value High
  Parental Health Value
• Healthy Lifestyle Choices 24.7
  38.7
• Difference
  14.0
• .
• Outcome 1
• Parents Role Model Unhealthy
  Parents Role Model Healthy Choices
• Parents Health Value Low High
  Low High
• Healthy Choices 14.9 34.0
  33.0 52.6
• Difference
  19.1 19.6

15
MeansOutcome 2

• Original Difference
• Low Parental Health Value High
  Parental Health Value
• Healthy Lifestyle Choices 24.7
  38.7
• Difference
  14.0
• .
• Outcome 2
• Parents Role Model Unhealthy Choices
  Parents Role Model Healthy Choices
• Parents Health Value Low High
  Low High
• Healthy Choices 22.3 36.6
  25.5 39.8
• Difference 14.3
  14.3

16
MeansOutcome 3

• Original Difference
• Low Parental Health Value High
  Parental Health Value
• Healthy Lifestyle Choices 24.7
  38.7
• Difference
  14.0
• .
• Outcome 3
• Parents Role Model Unhealthy Choices
  Parents Role Model Healthy Choices
• Parents Health Value Low High
  Low High
• Healthy Choices 15.6 22.7
  34.2 41.0
• Difference 7.1
  6.8

17
MeansOutcome 4

• Original Difference
• Low Parental Health Value High
  Parental Health Value
• Healthy Lifestyle Choices 24.7
  38.7
• Difference
  14.0
• .
• Outcome 4
• Parents Role Model Unhealthy Choices
  Parents Role Model Healthy Choices
• Parents Health Value Low High
  Low High
• Healthy Choices 23.5 24.8
  37.7 39.2
• Difference 1.3
  1.5

18
MeansOutcome 5

• Original Difference
• Low Parental Health Value High
  Parental Health Value
• Healthy Lifestyle Choices 24.7
  38.7
• Difference
  14.0
• .
• Outcome 5
• Parents Role Model Unhealthy Choices
  Parents Role Model Healthy Choices
• Parents Health Value Low High
  Low High
• Healthy Choices 16.4 31.3
  38.9 40.1
• Difference
  14.9 1.2