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ISYE 6501 Midterm 1|High Quality
Questions With Verified Solutions 2026
What does the C value do in a CUSUM model? - correct-answer-It pulls the Xt
down a bit as we expect Xt to be higher than expectation at random.
The bigger C is, the harder it is for St to get large, and the less sensitive the
method will be.
The smaller C is the more sensitive the model will be.
How to find correct C (pulls Xt down a bit) and T (threshold for change detected)
in CUSUM model? - correct-answer-how costly it is if the model takes a long time
to notice a change and how costly it is if the model thinks its found a change that
doesn't exist.
Control chart for CUSUM - correct-answer-plots St over time and if it ever gets
beyond the threshold T line it shows CUSUM has detected a change.
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Exponential Smoothing - correct-answer-used for analyzing time series data
where the respons is known for many time periods
Notes:
- modeling an assortment of variations and also dealing with randomness
- difficult to find a baseline
Exponential Smoothing data explanation - correct-answer-St: expected baseline
response at time period t
Xt: observed response
How exponential smoothing identifies change - correct-answer-Merges two ways
of thinking: St = Xt and St = St-1
so St = alpha*xt + (1-alpha)St-1
where 0<alpha<1
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if alpha approaches 0 there is a lot of randomness in the system
if alpha approaches 1 not much randomness
How to start and continue with exponential smoothing? - correct-answer-Initial
condition is S1 = x1 (doesn't deal with trends or cyclical variations)
Future includes trends and cyclical variation
How do trends effect exponential smoothing? - correct-answer-Tt is the trend at
time period t
Add it to the (1 - alpha) section of exponential smoothing to yesterdays St (St-1).
Initial condition is T1 = 0
Cyclic patterns - correct-answer-similar to trend as it has an additive component
to the exponential smoothing formula.
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When we use a cyclic factor to inflate or deflate our observed value, we use the
cyclic factor from L (length of cycle) time periods ago. Because that's the most
recent cyclic factor we have from the same part of the cycle.
If C is 1.1 on Sunday then sales were 10% higher just because it's Sunday. Of 550
sold on Sunday, 500 is basline and 50 is 10% extra.
What is triple exponential smoothing - correct-answer-Holt-Winters method
What is single exponential smoothing? - correct-answer-Trends, seasonality --
work exactly the same way
How does xt (observed response) vary the St in exponential smoothing? - correct-
answer-When xt is high, St is not as high as it is pulled down by (1 - alpha)St-1
When xt is low, St is not as low as it is pulled up by (1-alpha)St-1.
ISYE 6501 Midterm 1|High Quality
Questions With Verified Solutions 2026
What does the C value do in a CUSUM model? - correct-answer-It pulls the Xt
down a bit as we expect Xt to be higher than expectation at random.
The bigger C is, the harder it is for St to get large, and the less sensitive the
method will be.
The smaller C is the more sensitive the model will be.
How to find correct C (pulls Xt down a bit) and T (threshold for change detected)
in CUSUM model? - correct-answer-how costly it is if the model takes a long time
to notice a change and how costly it is if the model thinks its found a change that
doesn't exist.
Control chart for CUSUM - correct-answer-plots St over time and if it ever gets
beyond the threshold T line it shows CUSUM has detected a change.
,2|Page
Exponential Smoothing - correct-answer-used for analyzing time series data
where the respons is known for many time periods
Notes:
- modeling an assortment of variations and also dealing with randomness
- difficult to find a baseline
Exponential Smoothing data explanation - correct-answer-St: expected baseline
response at time period t
Xt: observed response
How exponential smoothing identifies change - correct-answer-Merges two ways
of thinking: St = Xt and St = St-1
so St = alpha*xt + (1-alpha)St-1
where 0<alpha<1
,3|Page
if alpha approaches 0 there is a lot of randomness in the system
if alpha approaches 1 not much randomness
How to start and continue with exponential smoothing? - correct-answer-Initial
condition is S1 = x1 (doesn't deal with trends or cyclical variations)
Future includes trends and cyclical variation
How do trends effect exponential smoothing? - correct-answer-Tt is the trend at
time period t
Add it to the (1 - alpha) section of exponential smoothing to yesterdays St (St-1).
Initial condition is T1 = 0
Cyclic patterns - correct-answer-similar to trend as it has an additive component
to the exponential smoothing formula.
, 4|Page
When we use a cyclic factor to inflate or deflate our observed value, we use the
cyclic factor from L (length of cycle) time periods ago. Because that's the most
recent cyclic factor we have from the same part of the cycle.
If C is 1.1 on Sunday then sales were 10% higher just because it's Sunday. Of 550
sold on Sunday, 500 is basline and 50 is 10% extra.
What is triple exponential smoothing - correct-answer-Holt-Winters method
What is single exponential smoothing? - correct-answer-Trends, seasonality --
work exactly the same way
How does xt (observed response) vary the St in exponential smoothing? - correct-
answer-When xt is high, St is not as high as it is pulled down by (1 - alpha)St-1
When xt is low, St is not as low as it is pulled up by (1-alpha)St-1.
