Time To Missed Exercise

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Time To Missed Exercise

• Farrokh Alemi, Ph.D.

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Why do it?

• You need to distinguish between random days of
  missed exercise from real changes in underlying
  exercise patterns

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Steps in construction of days of missed exercise

• Verify assumptions
• Collect data
• Calculate time to failure
• Calculate control limits
• Plot chart
• Interpret findings
• Display chart

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Step 1 Check assumptions

• One observation per day
• Everyday is a new day.
• Exercise on one day does not affect exercise on
  other days
• Successes are more frequent than failures
• Longer stretches of missed exercise are more rare

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Step 2 Collect data

• Decide what is your exercise plan
• Keep a diary
• Record for each day if you kept to your plans
• Keep notes of major changes in your life style

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Step 3 Calculate length of missed plans
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Step 4 Calculate control limits

• R is the ratio of failure days to success days 
• UCL R 3 R (1R) 0.5

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Step 5 Plot control chart

• X-axis is time
• Y-axis is either length of failures
• UCL is drawn as straight line

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Steps 6 7 Interpret findings display chart

• Any series of failures exceeding UCL cannot be
  due to chance.
• It is a real change in exercise patterns
• Display chart
• For yourself
• For others

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Example

• 35 year old female kept daily record of keeping
  to exercise plans for 18 days
• First week was pre-intervention
• Failures occurred on 2nd to 4th, 6th, 7th and
  16th day
• Is she improving?

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Calculate length of failures

• Set to 0 every time we succeed
• Set to one on first day of failure
• Increased when more than one consecutive day of
  failure

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Calculate ratio for post intervention period
1 days
Number of days of failure
.10
Ratio
Number of days of success
10 days
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Calculate upper control limit
UCL
Ratio 3 (Ratio(1Ratio)).5
UCL .1 3 (.1(1.1)).5 1.09
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Plot chart
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Interpret findings display

• Lots of long failures before the intervention
• No significant failures since the intervention