6.1 Quick revision
A new method for evaluating bridge loads (O’Brien et al. 2018) used a simulation to compare the new method to an existing method. For the simulation, they modelled the gross vehicle mass (GVM) of trucks as having a normal distribution, with a mean of 13 tonnes and a standard deviation of 1.3 tonnes.
The Isuzu F-Series trucks are rated as having a GVM between 10.7 and 26.0 tonnes (depending on the configuration).
- What is the \(z\)-score for the lower limit of 10.7 tonnes?
- What is the \(z\)-score for the upper limit of 26.0 tonnes?
- A negative \(z\)-score means that the mean has a smaller value than the standard deviation. True of false?
- A standard error measures the size of the difference between the sample proportion and the population proportion. True of false?
- \(z = (10.7 - 13)\div 1.3 = -1.77\).
- \(z = (26.0 -13)/1.3 = 10\).
- A negative \(z\)-score means that the value is less than the mean.
- The standard error measures how much a sample value is likely to vary from sample to sample.