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Exercise

Calculating a z-score

Since variables have arbitrary ranges and units, we need to standardize them. For example, it would be silly if a hypothesis test gave a different answer if your variables were in Euros instead of US dollars. Standardization avoids that.

One standardized value of interest in a hypothesis test is called a z-score. To calculate it, we need three numbers: the sample statistic (point estimate), the hypothesized statistic, and the standard error of the statistic (which we estimate from the bootstrap distribution).

The sample statistic is late_prop_samp.

late_shipments_boot_distn is a bootstrap distribution of the proportion of late shipments. The proportion of late shipments statistic is in the late_prop column.

late_prop_samp and late_shipments_boot_distn are available; dplyr is loaded.

Instructions
100 XP
  • Hypothesize that the proportion of late shipments is 6%.
  • Calculate the standard error. That is, the standard deviation of the bootstrap distribution.
  • Calculate the z-score.
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