A trade association with 3,500 members needs to know how many members should be sent e-mail invitations to participate in a study. The variability of the population is unknown, and the trade association wants to be 95% confident that the sample results fall within a margin of error of ± 3%.

Find an online sample calculator that takes into account the population size and response rate in addition to confidence level, variability of the population, and margin of error. Calculate the sample size needed and provide the URL of the sample size calculator used.