# Mean Absolute Deviation

• January 21st 2011, 01:44 AM
smashedpumpkins
Mean Absolute Deviation
I understand MAD, but I cannot figure out this question. Here's the information.

Daily high temperatures in St. Louis for the last week were as follows: 92, 91, 94, 95, 96, 88,90.
The mean absolute deviation based on a 2-day moving average = 3.20

How in the world is it 3.20? I've tried 100's of combinations to try to repeat this answer, but I can't do it. I'm 100% sure this is the correct answer. Can anyone please show me a step by step walk through on this problem? I've spent all day on this...
• January 21st 2011, 08:09 AM
emakarov
I've got something but am not 100% sure. They may be talking about a 2-day moving average forecasts and measuring these forecasts using MAD. Then the situation is as follows.

$\begin{array}{lrrrrrrr}
\mbox{Actual temperature} & 92 & 91 & 94 & 95 & 96 & 88 & 90\\
\mbox{2-day average forecast} & & & 91.5 & 92.5 & 94.5 & 95.5 & 92\\
\mbox{Absolute deviation} & & & 2.5 & 2.5 & 1.5 & 7.5 & 2
\end{array}$

The average of the last line is 3.2.
• January 21st 2011, 08:38 AM
ahaok
Quote:

Originally Posted by smashedpumpkins
I understand MAD, but I cannot figure out this question. Here's the information.

Daily high temperatures in St. Louis for the last week were as follows: 92, 91, 94, 95, 96, 88,90.
The mean absolute deviation based on a 2-day moving average = 3.20

How in the world is it 3.20? I've tried 100's of combinations to try to repeat this answer, but I can't do it. I'm 100% sure this is the correct answer. Can anyone please show me a step by step walk through on this problem? I've spent all day on this...

What is the question exactly?! do The values from last week ( 7 days) have something to do with MAD of those two days? Or 3.20 have been obtained from 2 new temperatures?
• January 21st 2011, 11:49 AM
smashedpumpkins
Quote:

Originally Posted by emakarov
I've got something but am not 100% sure. They may be talking about a 2-day moving average forecasts and measuring these forecasts using MAD. Then the situation is as follows.

$\begin{array}{lrrrrrrr}
\mbox{Actual temperature} & 92 & 91 & 94 & 95 & 96 & 88 & 90\\
\mbox{2-day average forecast} & & & 91.5 & 92.5 & 94.5 & 95.5 & 92\\
\mbox{Absolute deviation} & & & 2.5 & 2.5 & 1.5 & 7.5 & 2
\end{array}$

The average of the last line is 3.2.

Yep this is for forecasting. Ohhh wow. I guess I didn't understand 2-day moving average. I was trying everything I could with the last two numbers. I was even trying to divide them by 5. Now I see why it's 5 observations... I guess the keyword is "moving". Thanks a million!

Randy
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