Quandaries
and Queries 

Christie student grade OAC level math I was given a question with N=100, sample proportion is 0.1 compute the 95% confidence interval for P? I have tried this several ways but do not know how to do without means, standard deviations, standard error of the mean? I asked my teacher and she said I have all the info I need. Can you help???? 

Hi Christie, With a binomial distribution like the one you have the population is divided into two groups. It is sometimes helpful to think of the two group as zeros and ones. For example if a question on a survey to students says "Do you own a car?" then the researcher might record a one if you say yes and a zero if you say no. The researcher is interested in the proportion of students who own a car. This is the population proportion p. If you think of the population as zeros and ones then this p is the mean of the population. In your example the researcher asked n=100 students and got 10 who said yes. The researcher then has 10 ones and 90 zeros so the sample mean is 10/100 = 0.1 (the sample proportion). I don't know which expression you use to fand the sample variance but when did it I got a smaple variance of 0.3. Does this help? Penny 

