Choosing Test Statistics You now know three different statistics for comparing means: (1) the z for a sample mean, (2) the single sample t, and (3) the related samples t. See Appendix I for information on when to use each statistic. 1. Can people accurately judge how much time has passed? To answer this question a researcher asks 35 students to sit in a room, alone, doing nothing. At the end of 8 minutes, she asks the students to estimate how long they were in the room. The average estimate was 10.1 minutes with a standard deviation of 2.34 minutes. Did people accurately estimate time? 2. To determine if yoga makes people more flexible, a sports psychologist recruits 25 runners to participate in a study. He first measures the flexibility of each runner by seating them with their legs extended in front of them and seeing how far they can stretch. The scores are recorded in centimeters and are normally distributed. The 25 runners attend yoga classes three times a week and their flexibility is measured again. The mean score before yoga was 12.4 cm and the mean after yoga was 18.1 cm. Does flexibility increase after the yoga class? 3. A recent nationwide study revealed that people eat an average of just 2.9 servings of fruits and vegetables per day. A nutritionist wonders if people who live in areas where fresh fruits and vegetables are easy to grow year-round (e.g., California) eat more fruits and vegetables than the national average. To test this hypothesis, the nutritionist as