4.5 Relationships, trends and confounders

NCA-GENL · Data Analysis and Visualization (14% of the exam) · Official objective: “Identify relationships and trends or any factors that could affect the results of research.”

Spotting patterns and the factors that can distort results.

Key points

  1. NVIDIA warns that R² does not measure bias, so an overfitted model can have a high R², and you should also look at other metrics.

    What NVIDIA says (1)

    “Second, R² does not give any measure of bias, so you can have an overfitted (highly biased) model with a high value of R².”

    — A Comprehensive Overview of Regression Evaluation Metrics

  2. NVIDIA notes that data from a single institution can be biased by patient demographics, instruments or clinical specializations, which can affect the results of a model trained on it.

    What NVIDIA says (1)

    “Medical institutions have had to rely on their own data sources, which can be biased by, for example, patient demographics, the instruments used or clinical specializations.”

    — What Is Federated Learning?

  3. Cross-filtering replaces hand-written DataFrame queries with a graphical user interface (GUI). In NVIDIA's example, a clear pattern emerged between weekday and weekend trips.

    What NVIDIA says (2)

    “As shown in Figure 5, a clear pattern emerges between weekday and weekend trips”

    — Accelerated Data Analytics: A Guide to Data Visualization with RAPIDS

    “This approach replaces dataframe queries with a GUI tool.”

    — Accelerated Data Analytics: A Guide to Data Visualization with RAPIDS

Sample question

A model has a high R² on your data. Why might that still mislead you?

Show the answer

Answer: R² gives no measure of bias, so an overfitted model can still show a high R²; look at other metrics too

NVIDIA warns that R² does not measure bias, so an overfitted model can have a high R², and you should also look at other metrics.

What NVIDIA says (1)

“Second, R² does not give any measure of bias, so you can have an overfitted (highly biased) model with a high value of R².”

— A Comprehensive Overview of Regression Evaluation Metrics

Practice 4.5 (3 questions) Full Data Analysis and Visualization guide

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