Degrees of Freedom

[Yashin Ali]

Dear Sir,

Using the following code in Ngene, I am bit confused about how many parameters (K) are there (4-only the attributes or 5-including if i use B0) ?
In such case using the formula to achieve the minimum no. of choice tasks would be (J-1)*S>=k = (3-1)*S=4; S=2 ?

My experimental design consists of 3 alternatives, each with 4 attributes and having symmetrical design with 3 attribute level (considering a unlabeled design and using a generic parameters).

design
;alts = Tariff1*, Tariff2*, Tariff3*
;rows = 12
;eff= (mnl,d)
;alg = mfederov
;block= 2
;model:
U(Tariff1) = bloc[-0.000001] * Distance[500,1000,1500](4-6,4-6,4-6)
+brt [0.000001] * RWT[0,10,15](4-6,4-6,4-6)
+ bchargingspeed.dummy[0.0001|0.0001] * Chargingspeed[1,2,3] ? 1 = Medium(base), 2 = Fast, 3 = Rapid
+ bcost[-0.000001] * Price[55,75,95](4-6,4-6,4-6)
/
U(Tariff2) = bloc*Distance+brt*RWT+bchargingspeed*Chargingspeed+bcost*Price /
U(Tariff3) = bloc*Distance+brt*RWT+bchargingspeed*Chargingspeed+bcost*Price

$

[Michiel Bliemer]

The number of parameters consists of all the coefficients that you will be estimating in your model. In your case, this is 5, including the constant. So yes, the minimum number of rows you need is 2. this will allow you to estimate the model. However, this may not be sufficient to estimate more advanced models, so to guarantee sufficient variation in your data you would use a larger number of rows, and 12 should be sufficient in your case I recon.

Michiel