My hen 'Yolko Ovo' lays from 1 to 5 eggs per day. She?s equally likely to lay 1, 2, 3, 4, or 5 eggs. At the end of every week, I count how many eggs Yolko Ovo laid during the week, and write down her weekly total. I've been doing that for many years now. If I plot a histogram of these weekly totals, which of the following would it most closely resemble?

Question

BlackTom AI · Accepted Answer

Restating the scenario: Yolko Ovo lays between 1 and 5 eggs each day with equal probability, and we sum the eggs over a 7-day week to get a weekly total. The question asks what the histogram of these weekly totals would most closely resemble.

Option analysis:
- If we were to expect a normal distribution, we should justify why the sum of several independent, identically distributed random daily counts tends to be bell-shaped. Here, each day is an independent draw from a discrete uniform distribution on {1,2,3,4,5} with mean 3 and variance 2. Over a week, the total is the sum of 7 such independent daily counts.
- The central limit theorem tells us that the sum (or average) of a reasonably large number of independent random variables with finite mean and variance tends to a normal distribution, regardless of the original distribution shape. While seven days is not extremely large, it is enough for the weekly total to start looking near-normal, especially since the daily distribution is symmetric and bounded.
- Calculating key parameters helps contextualize the shape: the weekly mean is 7 × 3 = 21, and the weekly variance is 7 × 2 = 14, giving a standard deviation of about sqrt(14) ≈ 3.74. The possible weekly totals range from 7 (all days 1) to 35 (all days 5). With these finite bounds and the additive nature of the sum, the histogram would be centered around 21 and exhibit a roughly bell-shaped dispersion around that center, rather than a flat, uniform, or highly skewed shape.

Why this reasoning supports the chosen conclusion:
- The daily counts are not normally distributed themselves, but the sum over 7 days tends toward normality due to the central limit theorem.
- The distribution will be approximately bell-shaped rather than strictly uniform or heavily skewed, given the aggregation of independent daily outcomes.

Why other potential interpretations would be incorrect (if exploring alternative options):
- It would not be uniform: a uniform weekly total would require each value to be equally likely across a wide range, which is not the case when summing independent bounded variables.
- It would not be highly skewed: the daily distribution is symmetric around 3, and summing symmetric, bounded variables tends to produce a symmetric, bell-like shape around the weekly mean.
- It would not be bimodal or exotic: with independent daily counts, the total tends to smooth out into a single peak near the mean as the number of days increases.

PSYC20007_2025_SM2 Goals of Statistical Testing II

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