Posted: November 26th, 2016

- An investigator felt that the sample size of the presented data set is too small for the conduction of a hypothesis test. He calculated the proportion of all negative outcomes in the data set for the working mothers (any outcome that is not full-term and normal birth weight), and considered that proportion a reasonable estimate of the prevalence of negative outcomes. Using this estimate of p, what minimum sample size is needed for his new planned study (assuming that a 95% confidence interval will be used and that the margin of error is within 2% of the population proportion)?

- Assume that the investigator collected a sample of 1000 working pregnant women and followed them till the end of their pregnancy. The following data in the table were observed:

Full-term newborn | Preterm newborn | Abortion or Stillbirth | Total | |

Working for < 40 hours/week | 487 | 122 | 41 | 650 |

Working for ≥ 40 hours/week | 135 | 162 | 53 | 350 |

Total | 622 | 284 | 94 | 1000 |

Please, use the data in the previous table and determine if there is a statistical significant relation between working for long hours and the occurrence of negative pregnancy outcomes.

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