Function to determine required sample size to be within a given margin of error.

`nsize(b, sigma = NULL, p = 0.5, conf.level = 0.95, type = "mu")`

- b
the desired bound.

- sigma
population standard deviation. Not required if using type

`"pi"`

.- p
estimate for the population proportion of successes. Not required if using type

`"mu"`

.- conf.level
confidence level for the problem, restricted to lie between zero and one.

- type
character string, one of

`"mu"`

or`"pi"`

, or just the initial letter of each, indicating the appropriate parameter. Default value is`"mu"`

.

Returns required sample size.

Answer is based on a normal approximation when using type `"pi"`

.

```
nsize(b=.03, p=708/1200, conf.level=.90, type="pi")
#>
#> The required sample size (n) to estimate the population
#> proportion of successes with a 0.9 confidence interval
#> so that the margin of error is no more than 0.03 is 728 .
#>
#>
# Returns the required sample size (n) to estimate the population
# proportion of successes with a 0.9 confidence interval
# so that the margin of error is no more than 0.03 when the
# estimate of the population propotion of successes is 708/1200.
# This is problem 5.38 on page 257 of Kitchen's BSDA.
nsize(b=.15, sigma=.31, conf.level=.90, type="mu")
#>
#> The required sample size (n) to estimate the population
#> mean with a 0.9 confidence interval so that the margin
#> of error is no more than 0.15 is 12 .
#>
#>
# Returns the required sample size (n) to estimate the population
# mean with a 0.9 confidence interval so that the margin
# of error is no more than 0.15. This is Example 5.17 on page
# 261 of Kitchen's BSDA.
```