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ASR Statistical Significance Testing

Perform statistical testing on word error rates(WER) between ASR models using the bootstrap method. This library computes the confidence interval (CI) between the WER difference of two competing Automatic speech recognition (ASR) models X and Y.

The implementation is based on these two papers; Bootstrap estimates for confidence intervals in ASR performance evaluation and Statistical Testing on ASR Performance via Blockwise Bootstrap.

How to use

For each model X and Y, compute total errors and count of words for each sentence in your test set. Then save them in a text file with a seperator. For example, for a sentence in the test set;

model A: 5 errors model B: 10 errors total number of words in sentence: 12

Save as 5|10|12 where "|" is used as a separator. If you intend to use blockwise sampling, e.g. sampling on speakers, then save as 5|10|12|speaker_id

Checkout the test_files directory for example files.

To find out if model Y is better than model X;

    cd asr_stat_significance
    import numpy as np
    np.random.seed(42)
    
    from asr_stat_significance import StatisticalSignificance

    si_obj = StatisticalSignificance(
        file_path="wer_file.txt", 
        total_batch=1000,
        use_gaussian_appr=True,
    )
    ci_obj  = si_obj.compute_significance(
                        num_samples_per_batch=30, confidence_level=0.95)
    print(ci_obj)
    print(f"The difference in WER between Model X and Y is significant: ", {ci_obj.is_significant()})

OR when you would like to perform bootstrap sampling based on some criteria such as speaker, gender, or age, etc.

    import numpy as np
    np.random.seed(42)
    
    from asr_stat_significance import StatisticalSignificance

    si_obj_block = StatisticalSignificance(
        file_path="wer_file_block.txt", 
        total_batch=1000,
        use_gaussian_appr=True,
    )
    ci_obj_block  = si_obj_block.compute_significance(num_samples_per_block=2, 
                                                confidence_level=0.95, use_blockwise_bootstrap=True,)
    print(ci_obj_block)
    print(f"The difference in WER between Model X and Y is significant: ", {ci_obj_block.is_significant()})

How to interprete the CI values

If both values of CI low and CI high lie fully on the negative side on the real axis (i.e., if both values are negative), then, at the confidence level specified, the difference in WER is statistically significant. Therefore, one can say model Y is better than model X.

Function parameters

  • confidence_level: Confidence level to be used for computation. Typical levels include 90%, 95% and 99%. Default is 95%.
  • total_batch: total amount of bootstrap sampling runs. Note that sampling is done with replacement. Typical values are 10^2, 10^3, 10^4. Default is 10^3.
  • num_samples_per_batch: The number of WER/CER data selected for each batch. Value should be based on the size of the test set.
  • num_samples_per_block: If use_blockwise_bootstrap=True, then, this is the number of samples to collect from each block during bootstrap sampling.