Debugging Data Code

You're a Statistician at MSD, reviewing a colleague's helper function before it goes into the trial-reporting pipeline. It's meant to summarize a biomarker by dose group, including the placebo (0 mg) arm as its own group for comparison.

import pandas as pd

def summarize_trial(df, dose_col="dose_mg", result_col="biomarker_level", outliers=[]):
    outliers.append(None)

    df = df[df[dose_col] != 0]

    groups = df.groupby(dose_col)
    summary = pd.DataFrame()
    for name, group in groups:
        row = {
            "dose_mg": name,
            "n": len(group),
            "mean": group[result_col].mean(),
            "std": group[result_col].std(),
        }
        summary = summary.append(row, ignore_index=True)

    summary["is_significant"] = summary["mean"] == summary["mean"].max()

    return summary

Walk through how you'd debug this, what breaks and when, and what you'd change before it's trusted for a trial report.