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Two population Threshold Wise Testing procedure

Source: R/two-twt.R
TWT2.Rd

The function implements the Threshold Wise Testing procedure for testing mean differences between two functional populations. Functional data are tested locally and unadjusted and adjusted p-value functions are provided. The unadjusted p-value function controls the point-wise error rate. The adjusted p-value function controls the family-wise error rate asymptotically.

Usage

TWT2(
  data1,
  data2,
  mu = 0,
  dx = NULL,
  B = 1000L,
  paired = FALSE,
  alternative = c("two.sided", "less", "greater"),
  verbose = FALSE
)

twt2(
  data1,
  data2,
  mu = 0,
  dx = NULL,
  n_perm = 1000L,
  paired = FALSE,
  alternative = c("two.sided", "less", "greater"),
  verbose = FALSE
)

Arguments

data1

Either a numeric matrix or an object of class fda::fd specifying the data in the first sample. If the data is provided within a matrix, it should be of shape \(n_1 \times J\) and it should contain in each row one of the \(n_1\) functions in the sample and in columns the evaluation of each function on a same uniform grid of size \(J\).

data2

Either a numeric matrix or an object of class fda::fd specifying the data in the second sample. If the data is provided within a matrix, it should be of shape \(n_2 \times J\) and it should contain in each row one of the \(n_2\) functions in the sample and in columns the evaluation of each function on a same uniform grid of size \(J\).

mu

Either a numeric value or a numeric vector or an object of class fda::fd specifying the functional mean difference under the null hypothesis. If mu is a constant, then a constant function is used. If mu is a numeric vector, it must correspond to evaluation of the mean difference function on the same grid that has been used to evaluate the data samples. Defaults to 0.

dx

A numeric value specifying the discretization step of the grid used to evaluate functional data when it is provided as objects of class fda::fd. Defaults to NULL, in which case a default value of 0.01 is used which corresponds to a grid of size 100L. Unused if functional data is provided in the form of matrices.

B

An integer value specifying the number of iterations of the MC algorithm to evaluate the p-value of the permutation tests. Defaults to 1000L.

paired

A boolean value specifying whether a paired test should be performed. Defaults to FALSE.

alternative

A string specifying the type of alternative hypothesis. Choices are "two.sided", "less" or "greater". Defaults to "two.sided".

verbose

A boolean value specifying whether to print the progress of the computation. Defaults to FALSE.

n_perm

An integer value specifying the number of permutations for the permutation tests. Defaults to 1000L.

Value

An object of class ftwosample containing the following components:

  • data: A numeric matrix of shape \(n \times J\) containing the evaluation of the \(n = n_1 + n_2\) functions on a common uniform grid of size \(p\).

  • group_labels: An integer vector of size \(n = n_1 + n_2\) containing the group membership of each function.

  • mu: A numeric vector of shape \(J\) containing the evaluation of the functional mean difference under the null hypothesis on the same uniform grid used to evaluate the functional samples.

  • unadjusted_pvalues: A numeric vector of size \(J\) containing the evaluation of the unadjusted p-value function on the same uniform grid used to evaluate the functional samples.

  • adjusted_pvalues: A numeric vector of size \(J\) containing the evaluation of the adjusted p-value functione on the same uniform grid used to evaluate the functional samples.

Optionally, the list may contain the following components:

  • global_pvalue: A numeric value containing the global p-value. Only present if the correction argument is set to "Global".

  • pvalue_matrix: A numeric matrix of shape \(p \times p\) containing the p-values of the interval-wise tests. Element \(i, j\) contains the p-value of the test performed on the interval indexed by \(j, j+1 , \dots, j+(p-i)\). Only present if the correction argument is set to "IWT".

References

Abramowicz, K., Pini, A., Schelin, L., Stamm, A., & Vantini, S. (2022). “Domain selection and familywise error rate for functional data: A unified framework. Biometrics 79(2), 1119-1132.

Pini, A., & Vantini, S. (2017). Interval-wise testing for functional data. Journal of Nonparametric Statistics, 29(2), 407-424.

See also

See also plot.ftwosample() for plotting the results.

Examples

# Performing the TWT for two populations
TWT_result <- TWT2(NASAtemp$paris, NASAtemp$milan)

# Plotting the results of the TWT
plot(
  TWT_result,
  xrange = c(0, 12),
  title = 'TWT results for testing mean differences'
)


# Selecting the significant components at 5% level
which(TWT_result$adjusted_pvalues < 0.05)
#>   [1]  49  50  61  64  65  69  70  71  72  73  74  81  88  89  90  91  92  93
#>  [19]  94  95  96  97 101 102 103 104 105 106 107 108 109 110 111 112 113 114
#>  [37] 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132
#>  [55] 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150
#>  [73] 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168
#>  [91] 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186
#> [109] 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204
#> [127] 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222
#> [145] 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240
#> [163] 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258
#> [181] 259 260 261 262 264 265 266 267 269 270 271 272 273 274 275 276 281 286
#> [199] 288 289 290 291 299