The following data were collected in an experiment designed to investigate the impact of different positions of the mother on fetal heart rate. Fetal heart rate is measured by ultrasound in beats per minute. The study included 20 women who were assigned to one position and had the fetal heart rate measured in that position. Each woman was between 28-32 weeks gestation. The data are shown below.

Back     Side     Sitting     Standing
20         21          24           26
24         23          25           25
26         25          27           28
21         24          28           29
19         16          24           25

Is there a significant difference in mean fetal heart rates by position? Run the test at a 5% level of significance.