The population of the giraffe-necked weevil, pictured here, is distributed over hundreds of rainforest patches of eastern Madagascar. To estimate mean neck length of males (which is much longer than in females), researchers visited two rainforest patches and measured a total of 98 individuals: 50 sampled from one locality and 48 from the other. They calculated a 95% confidence interval for the mean from these data, using a sample size of 98. What assumption(s) of the confidence interval of the population mean were violated in making this calculation?