Specificity¶

Module Interface¶

class torchmetrics.Specificity(num_classes=None, threshold=0.5, average='micro', mdmc_average=None, ignore_index=None, top_k=None, multiclass=None, **kwargs)[source]

Computes Specificity:

$\text{Specificity} = \frac{\text{TN}}{\text{TN} + \text{FP}}$

Where $\text{TN}$ and $\text{FP}$ represent the number of true negatives and false positives respecitively. With the use of top_k parameter, this metric can generalize to Specificity@K.

The reduction method (how the specificity scores are aggregated) is controlled by the average parameter, and additionally by the mdmc_average parameter in the multi-dimensional multi-class case. Accepts all inputs listed in Input types.

Parameters

num_classes¶ (Optional[int]) – Number of classes. Necessary for 'macro', 'weighted' and None average methods.
threshold¶ (float) – Threshold probability value for transforming probability predictions to binary (0,1) predictions, in the case of binary or multi-label inputs.
average¶ (str) –
Defines the reduction that is applied. Should be one of the following:
- 'micro' [default]: Calculate the metric globally, across all samples and classes.
- 'macro': Calculate the metric for each class separately, and average the metrics across classes (with equal weights for each class).
- 'weighted': Calculate the metric for each class separately, and average the metrics across classes, weighting each class by its support (tn + fp).
- 'none' or None: Calculate the metric for each class separately, and return the metric for every class.
- 'samples': Calculate the metric for each sample, and average the metrics across samples (with equal weights for each sample).
Note

What is considered a sample in the multi-dimensional multi-class case depends on the value of mdmc_average.
mdmc_average¶ (Optional[str]) –
Defines how averaging is done for multi-dimensional multi-class inputs (on top of the average parameter). Should be one of the following:
- None [default]: Should be left unchanged if your data is not multi-dimensional multi-class.
- 'samplewise': In this case, the statistics are computed separately for each sample on the N axis, and then averaged over samples. The computation for each sample is done by treating the flattened extra axes ... (see Input types) as the N dimension within the sample, and computing the metric for the sample based on that.
- 'global': In this case the N and ... dimensions of the inputs (see Input types) are flattened into a new N_X sample axis, i.e. the inputs are treated as if they were (N_X, C). From here on the average parameter applies as usual.
ignore_index¶ (Optional[int]) – Integer specifying a target class to ignore. If given, this class index does not contribute to the returned score, regardless of reduction method. If an index is ignored, and average=None or 'none', the score for the ignored class will be returned as nan.
top_k¶ (Optional[int]) –
Number of the highest probability entries for each sample to convert to 1s - relevant only for inputs with probability predictions. If this parameter is set for multi-label inputs, it will take precedence over threshold. For (multi-dim) multi-class inputs, this parameter defaults to 1.

Should be left unset (None) for inputs with label predictions.
multiclass¶ (Optional[bool]) – Used only in certain special cases, where you want to treat inputs as a different type than what they appear to be. See the parameter’s documentation section for a more detailed explanation and examples.
kwargs¶ (Dict[str, Any]) – Additional keyword arguments, see Advanced metric settings for more info.

Raises

ValueError – If average is none of "micro", "macro", "weighted", "samples", "none", None.

Example

>>> from torchmetrics import Specificity
>>> preds  = torch.tensor([2, 0, 2, 1])
>>> target = torch.tensor([1, 1, 2, 0])
>>> specificity = Specificity(average='macro', num_classes=3)
>>> specificity(preds, target)
tensor(0.6111)
>>> specificity = Specificity(average='micro')
>>> specificity(preds, target)
tensor(0.6250)

Initializes internal Module state, shared by both nn.Module and ScriptModule.

compute()[source]

Computes the specificity score based on inputs passed in to update previously.

Returns

If average in ['micro', 'macro', 'weighted', 'samples'], a one-element tensor will be returned
If average in ['none', None], the shape will be (C,), where C stands for the number of classes

Return type

The shape of the returned tensor depends on the average parameter

Functional Interface¶

torchmetrics.functional.specificity(preds, target, average='micro', mdmc_average=None, ignore_index=None, num_classes=None, threshold=0.5, top_k=None, multiclass=None)[source]

Computes Specificity

$\text{Specificity} = \frac{\text{TN}}{\text{TN} + \text{FP}}$

Where $\text{TN}$ and $\text{FP}$ represent the number of true negatives and false positives respecitively. With the use of top_k parameter, this metric can generalize to Specificity@K.

The reduction method (how the specificity scores are aggregated) is controlled by the average parameter, and additionally by the mdmc_average parameter in the multi-dimensional multi-class case. Accepts all inputs listed in Input types.

Parameters

preds¶ (Tensor) – Predictions from model (probabilities, or labels)
target¶ (Tensor) – Ground truth values
average¶ (str) –
Defines the reduction that is applied. Should be one of the following:
- 'micro' [default]: Calculate the metric globally, across all samples and classes.
- 'macro': Calculate the metric for each class separately, and average the metrics across classes (with equal weights for each class).
- 'weighted': Calculate the metric for each class separately, and average the metrics across classes, weighting each class by its support (tn + fp).
- 'none' or None: Calculate the metric for each class separately, and return the metric for every class.
- 'samples': Calculate the metric for each sample, and average the metrics across samples (with equal weights for each sample).
Note

What is considered a sample in the multi-dimensional multi-class case depends on the value of mdmc_average.

Note

If 'none' and a given class doesn’t occur in the preds or target, the value for the class will be nan.
mdmc_average¶ (Optional[str]) –
Defines how averaging is done for multi-dimensional multi-class inputs (on top of the average parameter). Should be one of the following:
- None [default]: Should be left unchanged if your data is not multi-dimensional multi-class.
- 'samplewise': In this case, the statistics are computed separately for each sample on the N axis, and then averaged over samples. The computation for each sample is done by treating the flattened extra axes ... (see Input types) as the N dimension within the sample, and computing the metric for the sample based on that.
- 'global': In this case the N and ... dimensions of the inputs (see Input types) are flattened into a new N_X sample axis, i.e. the inputs are treated as if they were (N_X, C). From here on the average parameter applies as usual.
ignore_index¶ (Optional[int]) – Integer specifying a target class to ignore. If given, this class index does not contribute to the returned score, regardless of reduction method. If an index is ignored, and average=None or 'none', the score for the ignored class will be returned as nan.
num_classes¶ (Optional[int]) – Number of classes. Necessary for 'macro', 'weighted' and None average methods.
threshold¶ (float) – Threshold probability value for transforming probability predictions to binary (0,1) predictions, in the case of binary or multi-label inputs
top_k¶ (Optional[int]) –
Number of highest probability entries for each sample to convert to 1s - relevant only for inputs with probability predictions. If this parameter is set for multi-label inputs, it will take precedence over threshold. For (multi-dim) multi-class inputs, this parameter defaults to 1.

Should be left unset (None) for inputs with label predictions.
multiclass¶ (Optional[bool]) – Used only in certain special cases, where you want to treat inputs as a different type than what they appear to be. See the parameter’s documentation section for a more detailed explanation and examples.

Return type

Tensor

Returns

The shape of the returned tensor depends on the average parameter

If average in ['micro', 'macro', 'weighted', 'samples'], a one-element tensor will be returned
If average in ['none', None], the shape will be (C,), where C stands for the number of classes

Raises

ValueError – If average is not one of "micro", "macro", "weighted", "samples", "none" or None
ValueError – If mdmc_average is not one of None, "samplewise", "global".
ValueError – If average is set but num_classes is not provided.
ValueError – If num_classes is set and ignore_index is not in the range [0, num_classes).

Example

>>> from torchmetrics.functional import specificity
>>> preds  = torch.tensor([2, 0, 2, 1])
>>> target = torch.tensor([1, 1, 2, 0])
>>> specificity(preds, target, average='macro', num_classes=3)
tensor(0.6111)
>>> specificity(preds, target, average='micro')
tensor(0.6250)