How do I put days of the week into a multiple regression model?

[Paula]

I am building a multiple linear regression model to predict peak power demant
using maximum daily temerature (in degrees) and the day of the week as
independent variables. I am unsure how to code the days of the week in order
to get the result I want. (when I use the days - the regression add-in tool
states that I'm not using the correct type of data, its non-numeric). I
believe this model will have 7 seperate independent variables, but am unsure
on how to get there.

 

[Ron Rosenfeld]

I am building a multiple linear regression model to predict peak power demant
using maximum daily temerature (in degrees) and the day of the week as
independent variables. I am unsure how to code the days of the week in order
to get the result I want. (when I use the days - the regression add-in tool
states that I'm not using the correct type of data, its non-numeric). I
believe this model will have 7 seperate independent variables, but am unsure
on how to get there.

Sunday = 1
Monday = 2

etc.

or, if you have actual dates, use the WEEKDAY worksheet function.


--ron

 

[Dav]

If I understand correctly coding Monday to 1, Tuesday to 2 etc will
create one variable for days of the week and assume that tuesday is
double monday! I don't think this is what you want.

You need to create 7 variables
One for each day eg 1 if monday 0 if not as one variable, 1 if tuesday
0 if not etc. Although arguably you could get way with six variables as
if it is not mon-sat it has to be sunday!
day mon tue wed thu fri sat sun
Monday,1,0,0,0,0,0,0
Tuesday,0,1,0,0,0,0,0
Wednesday,0,0,1,0,0,0,0
Thursday,0,0,0,1,0,0,0
Friday,0,0,0,0,1,0,0
Saturday,0,0,0,0,0,1,0
Sunday,0,0,0,0,0,0,1


Regards
Dav