Hello All.

Sounds as though this may be a reasonable question for the list. Hope so at least. Would greatly appreciate any feedback you might have on the subject.

We have an estimated 479,000 hunters in Ohio and we want to conduct a survey

to estimate such things as hunter success rates, participation rates, and

opinions on various issues related to deer management. The first question

of course, is how large of a sample? My former boss conducted a similar

survey and ended up with 3800 (actually he mailed surveys to 6700 hunters,

apparently he new that the response rate would be down around 45-55% and

took this into consideration when calculating the necessary sample size)

useable responses. I'm now getting ready to conduct a similar survey and

the question of sample size once again needs to be addressed. There was

little documentation on how he arrived at 6,700 or 3,800 for that matter, so

I'm left with coming up with my own estimate and of course justifying it.

In all of the STATS text books that I've been able to lay my hands on, they

all deal with minimum sample sizes for estimating the mean for a given

variable or a proportion. In each case, you're asked to specify a

confidence level (typically 95%) and also the bound or error that you are

willing to accept, for instance plus/minus 2.5lbs in the case of the average

weight of a particular strain of egg plant. In this survey that I plan on

running, I'm going to ask 40 questions. Am I to do this for every variable

and take the maximum sample size needed to achieve the desired level of

confidence or what? If not, is there a similar formula that one uses in

situations such as mine to come up with a sample size required for x-level

of confidence?

On a related note, after discussing this issue with a statistician in

*ia, he sent me an excel spreadsheet that asked for 2 inputs - the size

of the sample and the size of the population and the output was the maximum

% sampling error. The inputs and outputs are presented below.

Population Size Sample Size Max Sampling Error (95% CI) Percent Error

(95% CI)

479000.00 3800.00 0.0158345305 1.583453047

I'm having a tough time grasping just exactly what the 1.58% means (in

simple terms that adminstrators can understand!). Does that mean that in

repeated sampling of n=3800, 95 times out of 100, the sample mean plus or

minus 1.58% of the mean will contain the actual population mean? How, or

should I say, does this relate in anyway to the standard error and CV. I

know that the CV is actually a percentage (the SE expressed as a percent of

the mean). Is this 1.58% the maximum CV for all variables in the survey?

If anyone can help me sort this out, I would greatly appreciate it.

Thanks in advance for any assitance you might be able to offer.

Mike Tonkovich

Michael J. Tonkovich, Ph.D.

Wildlife Research Biologist

ODNR, Division of Wildlife