# Logistic Regression Problem - HELP!

#### aweimer

##### New Member
A local health clinic sent fliers to its clients to encourage everyone, but especially older persons at high risk of complications, to get a flue shot in time for protection against an expected flu epidemic. In a pilot follow-up study, 160 clients were randomly selected and asked whether they actually received a flu shot. In addition, data was collected on their health awareness, which was combined into a health awareness index, for which higher values indicate greater awareness. The estimated logistic regression model is
log(/(1-)) = -2.447 + 0.0568*(health awareness index)
where is the estimated probability that the client received a flu shot.

Estimate the health awareness index at which 48% of all clients receive a flu shot.
I said 42.469 and was incorrect.

Estimate the health awareness index at which the odds of receiving a flu shot are 2 to 3.

THANK YOU!

#### Dason

How did you get the answer 42.469?

#### aweimer

##### New Member
Would 48% be probability or odds?

I set up the problem like this: log(.48/1-.48)=-2.447+0.0568x and solved for x. so that x=42.469

Alternatively if I set up the problem like this: log(.48)=-2.447+0.0568x, I find that x=37.469

#### aweimer

##### New Member
For the second question, estimate the index for which the odds are 2 to 3 I did this:

log(2/3)=-2.447+0.0568x and found that x=39.981.

Does this seem correct? Do I find the log(odds) and solve for x for this type of problem?

#### Dason

Would 48% be probability or odds?
Estimate the health awareness index at which 48% of all clients receive a flu shot.
Sounds like probability to me...

I set up the problem like this: log(.48/1-.48)=-2.447+0.0568x and solved for x. so that x=42.469
I mentioned this before but... you gotta stop rounding in your intermediate steps. That's the right method but you're getting an answer thats off by almost an entire unit and I'm guessing it's because you're rounding everything to 1 or 2 decimal places in your intermediate steps.

#### aweimer

##### New Member
I'm doing this on a calculator and not rounding anything. Could my calculator be in the wrong setting?

#### aweimer

##### New Member
Do you know if I made a rounding error on the second part of this question as well?