Technical Ownership and Architectural Decisions Questions

import math
from typing import List, Tuple

def aggregate_and_ci(
    control_daily: List[Tuple[int,int]],   # list of (conversions, impressions)
    treat_daily:   List[Tuple[int,int]],
    z: float = 1.96
) -> dict:
    """
    Returns dict with control_rate, treat_rate, absolute_diff, rel_lift, and 95% CI for both absolute diff and relative lift.
    """
    def sum_counts(day_list):
        conv = sum(d[0] for d in day_list)
        imp  = sum(d[1] for d in day_list)
        return conv, imp

    c_conv, c_imp = sum_counts(control_daily)
    t_conv, t_imp = sum_counts(treat_daily)

    # protection against zero impressions
    if c_imp == 0 or t_imp == 0:
        raise ValueError("Impressions must be > 0 for both groups")

    p_c = c_conv / c_imp
    p_t = t_conv / t_imp

    abs_diff = p_t - p_c
    rel_lift = abs_diff / p_c if p_c > 0 else float('inf')

    # standard error for difference of proportions (unpooled)
    se = math.sqrt(p_c*(1-p_c)/c_imp + p_t*(1-p_t)/t_imp)
    lower_abs = abs_diff - z * se
    upper_abs = abs_diff + z * se

    # convert to relative lift CI safely
    if p_c > 0:
        lower_rel = lower_abs / p_c
        upper_rel = upper_abs / p_c
    else:
        lower_rel, upper_rel = float('-inf'), float('inf')

    return {
        "control_rate": p_c,
        "treat_rate": p_t,
        "absolute_diff": abs_diff,
        "abs_diff_95ci": (lower_abs, upper_abs),
        "relative_lift": rel_lift,
        "rel_lift_95ci": (lower_rel, upper_rel),
        "se_abs_diff": se
    }