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Different data sets often have unique means and standard deviations, making direct comparison difficult. The z‑score standardizes normally distributed data, enabling fair comparison and a consistent definition of percentiles across studies. While z‑scores can be found in reference tables, using a TI‑84 Plus calculator is faster, more accurate, and easier to follow. There are two reliable methods: (1) compute the mean and standard deviation of your list and then apply the z‑score formula, or (2) use the calculator’s invNorm function with the desired percentile as input. The same steps apply to the TI‑84 Plus Silver Edition as well.

Method 1: Using the Z‑Score Formula

1. Store your data as a list: press STAT, then select 1:Edit. The screen shows existing lists and an entry line.
2. Navigate to an empty list with the arrow keys and input each data point, pressing ENTER after each value.
3. Compute descriptive statistics: press STAT, arrow right to the statistics menu, select 1:1‑Var Stats, and press ENTER.
4. Ensure the list name matches the one you just edited. Leave FreqList blank.
5. Move the cursor to CALCULATE and press ENTER. The calculator displays the mean (∞) and standard deviation (σ). Record these two numbers.
6. Apply the z‑score formula: z = (x – mean) / SD, where x is any data point in your list.

Method 2: Using the invNorm Function

1. Open the distribution wizard: press 2ND then VARS to bring up the DISTR menu, select 3:invNorm, and press ENTER.
2. Enter the target percentile as a decimal next to the word area (e.g., 0.95 for the 95th percentile). Use the arrow keys to choose Paste and press ENTER.
3. Press ENTER again to compute the z‑score corresponding to that percentile. The calculator will display the result directly.

Both approaches give you a reliable z‑score. The first method is ideal when you have a raw data set, while the second is handy for quick percentile‑to‑z‑score conversions.