📚 Year 9 CIE Statistics: Key Terms & Quick Memorisation Guide | Year 9 CIE 统计：词汇术语速记指南
Welcome to your quick-reference guide for mastering essential statistical vocabulary in the Year 9 CIE curriculum. Building a solid foundation of terminology will help you interpret data, construct accurate graphs, and solve probability problems with confidence. Use this guide to memorise key terms effectively and avoid common mix-ups.
欢迎查阅为Year 9 CIE课程设计的统计核心词汇速记指南。牢固掌握术语将帮助你自信地解读数据、绘制准确图表并解决概率问题。请用本指南高效记忆关键概念，避免常见混淆。
1. Types of Data | 数据类型
In statistics, data is classified into two main types: qualitative (categorical) and quantitative (numerical). Qualitative data describes characteristics that cannot be measured numerically, such as eye colour or favourite sport. Quantitative data involves numbers and can be further divided into discrete and continuous. Discrete data can only take specific values, usually whole numbers (e.g., number of pets, shoe size). Continuous data can take any value within a range, typically measurements like height, weight, or time.
统计中，数据分为两大类型：定性（分类）数据和定量（数值）数据。定性数据描述无法用数字测量的特征，如眼睛颜色或最喜欢的运动。定量数据涉及数字，可进一步分为离散型和连续型。离散数据只能取特定值，通常是整数（如宠物数量、鞋码）。连续数据可在一定范围内取任意值，通常是测量值，如身高、体重或时间。
Recognising the data type guides your choice of graph: bar charts suit qualitative data, while histograms are for continuous quantitative data. Pictograms use symbols to represent counts but always need a key.
识别数据类型能指导你选择图表：条形图适合定性数据，直方图则用于连续定量数据。象形图用符号表示计数，但始终需要图例。
2. Averages: Mean, Median, Mode | 平均值：平均数、中位数、众数
The mean (often represented as x̄ value when data are sorted from smallest to largest; if there are two middle values, average them. The mode is the value that appears most often; a dataset can have more than one mode or no mode.
平均数（通常表示为 x̄）是算术平均值：将所有数值相加再除以数值个数。例如，2、4、9的平均数为 (2+4+9)÷3 = 5。中位数是将数据从小到大排序后位于中间的值；若有两个中间值则取它们的平均值。众数是出现次数最多的值；一组数据可以有多个众数或没有众数。
median position, use (n + 1) ÷ 2 for a list of n values. The mean is sensitive to outliers — 0}, mean = 22, but median = 3, making the median more representative of the typical value.
确定中位数的位置时，对n个数据使用 (n + 1) ÷ 2。平均数对异常值敏感——单个极端值就会使平均数偏离中心。在数据集{1, 2, 3, 4, 100}中，平均数为22，但中位数为3，因此中位数更能代表典型值。
- Mean = 'average' (add and divide)
- Median = 'middle' (order and pick centre)
- Mode = 'most' (frequency)
- 平均数 = “平均”（求和除以个数）
- 中位数 = “中间”（排序取中）
- 众数 = “最多”（出现频数最高）
3. Measures of Spread: Range and Quartiles | 离散程度：极差与四分位数
er quartile (Q₁) is the median of the lower half, the upper quartile (Q₃) is the median of the upper half. The interquartile range (IQR) = Q₃ − Q₁, which measures the spread of the middle 50% of the data and is resistant to outliers.
极差是最简单的离散度量：极差 = 最大值 − 最小值。四分位数将排序后的数据分为四等份。下四分位数（Q₁）是下半部分数据的中位数，上四分位数（Q₃）是上半部分的中位数。四分位距（IQR）= Q₃ − Q₁，衡量中间50%数据的分散程度，且不受异常值影响。
Remember: The median is also Q₂. When finding quartiles, always order the data first. For a small dataset, list the values, find the median, then find the medians of the two halves — do not include the overall median in the halves.
记住：中位数也是 Q₂。计算四分位数时务必先对数据排序。对于小数据集，列出数值后找出中位数，再分别找出上、下半部分的中位数——不要把总中位数包含进半部分中。
4. Frequency Tables and Class Intervals | 频数表与组距
occurs. For grouped continuous data, we define class intervals (e.g., 0 ≤ h < 10, 10 ≤ h <
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