One other question – when is the FPCF ignored?

Thanks

1. FPCF = (N – n)/N

2. FPCF = square root of (N – n) / (N -1)

3. FPCF = 1 – n/N, which is the same as #1

4. n’ = n / (1+ n/N), which means the FPCF = N / (N + n). n’ is the sample size after taking into account of FPCF.

Which one should I use?

I’m unfamiliar with the Finite Sample Correction, is it simply another term for the Finite Population Correction? I’ll assume it is as a google search seems to indicate so.

As 1000 is a lot less than 5% of 304 million, we will not need to use the Finite Population Correction Factor.

Accuracy is a reflection of the proportion of the sample size to the population. For instance, for a population of 1000, a sample size of 100 would theoretically be more accurate than a sample size of 10.

Back to your homework question, to retain the same level of accuracy, the proportion of the population captured in the sample would have to remain the same.

First, we find the proportion of sample size to total population in the initial survey:

1,000 / 304,000,000 = .0000032895.

Then, we multiply the new total population by this proportion to determine the new sample size required:

.0000032895 * 1,300,000,000 = 4276.32.

So the new sample size should be either 4276 or 4277 (depending if you round up or down) in order to maintain (roughly) the same accuracy.

Thanks..

Fiona

I deleted your comment listing your email address for your protection (spammers like to go around the internet find email addresses, you should avoid listing it publicly if possible).

On to your question, we utilize the FPCF to basically boost probability. When the sample is equal or great than 5%, we have a far greater chance that the sample’s data will apply to the population as a whole. In other words, we’re more confident that our data is correct and to show this extra confidence statistically we add the FPCF.

That’s the very general explanation. For a more detailed explanation, please re-read the last paragraph in my post above.

Hope that helps!

First, sorry it took me so long to respond. Your question got me a bit off guard and I had to dust off some cobwebs in regards to FPCF before answering it.

You use the FPCF because a) you’re sampling more than 5% of the population (in your case, 50% of the population is sampled) and b) you’re not replacing respondents after they are chosen.

What confidence interval are you using? Using a 95%, so a z of 1.96, the upper bound would be 103.92. It looks like you used a confidence interval of 92.65% with a z of 1.45 to get 102.9?