📚 IGCSE WJEC Statistics: Key Vocabulary Quick-Memory Guide | IGCSE WJEC 统计：词汇术语速记指南
In IGCSE WJEC Statistics, many marks are lost not because calculations are hard, but because key vocabulary is misunderstood or used loosely. This guide groups the essential statistical terms into memory-friendly sections, pairing each English definition with a clear Chinese explanation so you can revise quickly and answer exam questions precisely.
在 IGCSE WJEC 统计考试中，很多失分并不是因为计算难，而是因为关键词汇被误解或使用不严谨。本指南将核心统计术语按记忆友好的方式分组，并为每个英文定义配上清晰的中文解释，帮助你快速复习、准确作答。
1. Population, Sample and Census | 总体、样本与普查
In statistics, the population is the complete set of people, items or events that you are interested in. A sample is a subset of the population selected to represent it. A census collects data from every member of the population.
在统计中，总体是你所关注的全部人员、事物或事件的集合。样本是从总体中选出的、用于代表总体的子集。普查则从总体中的每一个成员处收集数据。
Remember: sample = part, census = all. If a question says 'every student in a school was asked', that is a census; if it says '50 students were chosen', that is a sample.
记住：样本 = 一部分，普查 = 全部。如果题目说 '学校里的每个学生都被询问'，那是普查；如果说 '选了 50 名学生'，那是样本。
Primary data are collected by you or for the purpose of the investigation. Secondary data are collected by someone else, such as government reports or previous surveys.
原始数据是由你或为了调查目的而收集的数据。二手数据是由他人收集的数据，例如政府报告或以前的调查。
2. Types of Data: Qualitative and Quantitative | 数据类型：定性数据与定量数据
Qualitative data describe qualities or categories that cannot be measured numerically, such as eye colour, gender or favourite subject. Quantitative data are numerical measurements or counts, such as height, mass, time or score.
定性数据描述无法用数字测量的属性或类别，例如眼睛颜色、性别或最喜欢的科目。定量数据是数值型的测量或计数，例如身高、质量、时间或分数。
antity (number). In WJEC questions, you may be asked to decide which type of data is shown in a table or chart.
速记提示：qualitative 对应性质或类别，quantitative 对应数量。在 WJEC 题目中，你可能会被要求判断表格或图表中显示的是哪一种数据类型。
Raw data are the original, unprocessed values before they are sorted, grouped or summarised. Once data are organised, they become easier to analyse but may lose individual detail.
原始数据是排序、分组或汇总之前的未处理数据。数据一旦被整理，就更容易分析，但可能丢失个别细节。
3. Discrete and Continuous Data | 离散数据与连续数据
Quantitative data can be split into discrete and continuous. Discrete data can only take separate values, usually counts, e.g. number of cars, goals, students. Continuous data can take any value within a range, usually measurements, e.g. height, temperature, time.
定量数据可分为离散数据和连续数据。离散数据只能取相互分离的值，通常是计数，例如汽车数量、进球数、学生人数。连续数据可以在一个范围内取任意值，通常是测量值，例如身高、温度、时间。
If you can count it, it is discrete. If you can measure it to any accuracy, it is continuous. Be careful: age in years might be discrete if recorded as whole years, but age measured exactly is continuous.
如果能数出来，就是离散的；如果能测量到任意精度，就是连续的。注意：按整岁记录的年龄是离散的，但精确测量的年龄是连续的。
lass intervals for continuous data are written with inequalities such as 150 ≤ h < 160.
许多错误来自把分组离散数据与连续数据混淆。在分组的频数表中，连续数据的组区间用不等式表示，例如 150 ≤ h < 160。
4. Averages: Mean, Median and Mode | 平均数：均值、中位数与众数
The three common averages are the mean, median and mode. The mean is the sum of all values divided by the number of values. The median is the middle value when data are ordered. The mode is the most frequent value.
三种常见的平均数是均值、中位数和众数。均值是所有数值之和除以数值个数。中位数是将数据排序后中间位置的值。众数是出现次数最多的值。
Use the formula for the mean carefully:
mean = (sum of all data values) ÷ n
使用均值公式时要仔细：均值 =（所有数据值之和）÷ n。
If there are two middle values for an even number of data, the median is the mean of those two middle values.
如果数据个数为偶数，有两个中间值，则中位数是这两个中间值的平均数。
The median is not affected by extreme values, but the mean is. The mode is useful for qualitative data where calculating a mean is impossible.
中位数不受极端值影响，但均值会受影响。众数对于无法计算均值的定性数据很有用。
5. Measures of Spread: Range, Quartiles and IQR | 离散程度：极差、四分位数与四分位距
d smallest values. It is a simple measure of spread: range = highest value − lowest value.
极差是最大值与最小值之间的差。它是离散程度的简单度量：极差 = 最大值 − 最小值。
Quartiles divide ordered data into four equal parts. The lower quartile Q1 is the median of the lower half; the upper quartile Q3 is the median of the upper half. The interquartile range (IQR) is Q3 − Q1 and describes the spread of the middle 50% of data.
四分位数将排序后的数据分成四等份。下四分位数 Q1 是下半部分的中位数；上四分位数 Q3 是上半部分的中位数。四分位距 IQR = Q3 − Q1，描述中间 50% 数据的离散程度。
WJEC questions often ask why IQR is more useful than range. Answer: IQR is not affected by extreme values, so it is a more reliable measure of spread.
WJEC 题目常问为什么四分位距比极差更有用。答案是：四分位距不受极端值影响，因此是更可靠的离散程度度量。
The range uses only two values, so it can be misleading if there is an outlier
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