Financial Risk Manager Part 1

Financial Risk Manager Part 1

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A mortgage analyst produced a model to predict housing starts (given in thousands) within Florida in the US. The time series model contains both a trend and a seasonal component and is given by the following:

yt=0.2Γ—Timet+10.5+3.0Γ—D2t+5.4Γ—D3t+0.7Γ—D4ty_t = 0.2 \times \text{Time}_t + 10.5 + 3.0 \times D_{2t} + 5.4 \times D_{3t} + 0.7 \times D_{4t}

The trend component is reflected in variable TIMEt\text{TIME}_t, where (t)=month(t) = \text{month}.

Seasons are defined as follows:

SeasonMonthsDummy
WinterDecember, January and February–
SpringMarch, April and MayD2tD_{2t}
SummerJune, July and AugustD3tD_{3t}
FallSeptember, October and NovemberD4tD_{4t}

The model starts in May 2019, i.e., y(T+1)y_{(T+1)} refers to June 2019. What does the model predict for September 2020?

TTanishq



Explanation:

Explanation

The model is given as:

yt=0.2Γ—Timet+10.5+3.0Γ—D2t+5.4Γ—D3t+0.7Γ—D4ty_t = 0.2 \times \text{Time}_t + 10.5 + 3.0 \times D_{2t} + 5.4 \times D_{3t} + 0.7 \times D_{4t}

Step 1: Determine the Time Period

  • The model starts in May 2019
  • y(T+1)y_{(T+1)} refers to June 2019
  • We need to find September 2020

From June 2019 to September 2020:

  • June 2019 to May 2020 = 12 months
  • June 2020 to September 2020 = 4 months
  • Total = 16 months

So September 2020 = y(T+16)y_{(T+16)}

Step 2: Identify the Seasonal Component

From the seasonal table:

  • September falls under Fall season
  • Fall season uses dummy variable D4tD_{4t}

Therefore, for September 2020:

  • D2t=0D_{2t} = 0 (not Spring)
  • D3t=0D_{3t} = 0 (not Summer)
  • D4t=1D_{4t} = 1 (Fall season)

Step 3: Calculate the Prediction

y(T+16)=0.2Γ—16+10.5+3.0Γ—0+5.4Γ—0+0.7Γ—1y_{(T+16)} = 0.2 \times 16 + 10.5 + 3.0 \times 0 + 5.4 \times 0 + 0.7 \times 1 y(T+16)=3.2+10.5+0+0+0.7y_{(T+16)} = 3.2 + 10.5 + 0 + 0 + 0.7 y(T+16)=14.4y_{(T+16)} = 14.4

Since housing starts are given in thousands, the model predicts approximately 14 housing starts in September 2020.

Key Points:

  • The intercept (10.5) represents the baseline for Winter season
  • Seasonal dummies add to this baseline for their respective seasons
  • The trend component (0.2 Γ— Time) captures the linear growth over time

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