Statistics: Principles and Methods, 7th Edition

9

Small Sample Inferences for Normal Populations

1 Student's t Distribution

2 Inferences about μ—Small Sample Size

3 Relationship between Tests and Confidence Intervals

4 Inferences about the Standard Deviation σ (The Chi-Square Distribution)

5 Robustness of Inference Procedures

Both capturing and measuring make data collection difficult.

Collecting a Sample of Lengths of Anacondas

Jesus Rivas, a herpetologist, is currently doing the definitive research on green anacondas. These snakes, some of the largest in the world, can grow to 25 feet in length. They have been known to swallow live goats and even people.

During the dry season Jesus Rivas and fellow researchers walk barefoot in shallow water in the Llanos grasslands shared by Venezuela and Colombia. When they feel a snake with their feet, they grab and hold it with the help of another person. After muzzling the snake with a sock and tape, they place a string along an imaginary centerline from head to tail. The measured length of string is the recorded length of the anaconda.

Females are typically larger than males. The lengths (feet) of 21 females are

If the captured snakes can be treated as a random sample, a 95% confidence interval for the mean length of a female anaconda in that area is given in the computer output