equiv_change_mean  R Documentation 
Checks for change in the mean value between a qualification data set and a sample. This is normally used to check for properties such as modulus. This function is a wrapper for a twosample t–test.
equiv_change_mean(
df_qual = NULL,
data_qual = NULL,
n_qual = NULL,
mean_qual = NULL,
sd_qual = NULL,
data_sample = NULL,
n_sample = NULL,
mean_sample = NULL,
sd_sample = NULL,
alpha,
modcv = FALSE
)
df_qual 
(optional) a data.frame containing the qualification data. Defaults to NULL. 
data_qual 
(optional) a vector of observations from the
"qualification" data to which equivalency is being tested. Or the column of

n_qual 
the number of observations in the qualification data to which the sample is being compared for equivalency 
mean_qual 
the mean from the qualification data to which the sample is being compared for equivalency 
sd_qual 
the standard deviation from the qualification data to which the sample is being compared for equivalency 
data_sample 
a vector of observations from the sample being compared for equivalency 
n_sample 
the number of observations in the sample being compared for equivalency 
mean_sample 
the mean of the sample being compared for equivalency 
sd_sample 
the standard deviation of the sample being compared for equivalency 
alpha 
the acceptable probability of a Type I error 
modcv 
a logical value indicating whether the modified CV approach
should be used. Defaults to 
There are several optional arguments to this function. Either (but not both)
data_sample
or all of n_sample
, mean_sample
and
sd_sample
must be supplied. And, either (but not both)
data_qual
(and also df_qual
if data_qual
is a column name and not a
vector) or all of n_qual
, mean_qual
and sd_qual
must
be supplied. If these requirements are violated, warning(s) or error(s) will
be issued.
This function uses a twosample ttest to determine if there is a difference in the mean value of the qualification data and the sample. A pooled standard deviation is used in the ttest. The procedure is per CMH171G.
If modcv
is TRUE, the standard deviation used to calculate the
thresholds will be replaced with a standard deviation calculated
using the Modified Coefficient of Variation (CV) approach.
The Modified CV approach is a way of adding extra variance to the
qualification data in the case that the qualification data has less
variance than expected, which sometimes occurs when qualification testing
is performed in a short period of time.
Using the Modified CV approach, the standard deviation is calculated by
multiplying CV_star * mean_qual
where mean_qual
is either the
value supplied or the value calculated by mean(data_qual)
and
CV*
is determined using calc_cv_star()
.
Note that the modified CV option should only be used if that data passes the Anderson–Darling test.
call
the expression used to call this function
alpha
the value of alpha passed to this function
n_sample
the number of observations in the sample for which
equivalency is being checked. This is either the value n_sample
passed to this function or the length of the vector data_sample
.
mean_sample
the mean of the observations in the sample for
which equivalency is being checked. This is either the value
mean_sample
passed to this function or the mean of the vector
datasample
.
sd_sample
the standard deviation of the observations in the
sample for which equivalency is being checked. This is either the value
mean_sample
passed to this function or the standard deviation of
the vector datasample
.
n_qual
the number of observations in the qualification data
to which the sample is being compared for equivalency. This is either
the value n_qual
passed to this function or the length of the
vector data_qual
.
mean_qual
the mean of the qualification data to which the
sample is being compared for equivalency. This is either the value
mean_qual
passed to this function or the mean of the vector
data_qual
.
sd_qual
the standard deviation of the qualification data to
which the sample is being compared for equivalency. This is either the
value mean_qual
passed to this function or the standard deviation
of the vector data_qual
.
modcv
logical value indicating whether the equivalency
calculations were performed using the modified CV approach
sp
the value of the pooled standard deviation. If
modecv = TRUE
, this pooled standard deviation includes the
modification to the qualification CV.
t0
the test statistic
t_req
the tvalue for \alpha / 2
and
df = n1 + n2 2
threshold
a vector with two elements corresponding to the
minimum and maximum values of the sample mean that would result in a
pass
result
a character vector of either "PASS" or "FAIL"
indicating the result of the test for change in mean
“Composite Materials Handbook, Volume 1. Polymer Matrix Composites Guideline for Characterization of Structural Materials,” SAE International, CMH171G, Mar. 2012.
calc_cv_star()
stats::t.test()
equiv_change_mean(alpha = 0.05, n_sample = 9, mean_sample = 9.02,
sd_sample = 0.15785, n_qual = 28, mean_qual = 9.24,
sd_qual = 0.162, modcv = TRUE)
## Call:
## equiv_change_mean(n_qual = 28, mean_qual = 9.24, sd_qual = 0.162,
## n_sample = 9, mean_sample = 9.02, sd_sample = 0.15785,
## alpha = 0.05,modcv = TRUE)
##
## For alpha = 0.05
## Modified CV used
## Qualification Sample
## Number 28 9
## Mean 9.24 9.02
## SD 0.162 0.15785
## Result PASS
## Passing Range 8.856695 to 9.623305
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