Edexcel GCSE Statistics - Key Terms Guaranteed Success

Edexcel GCSE Statistics - Key Terms Guaranteed Success What is a census? ️️A census is a survey of a whole population rather than just a small part of it What is a sample? ️️A sample is a survey of a small part of the population rather than the whole population Why do we use sampling? ️️We use samples because they are: • cheaper, • quicker and • easier to manage than using the whole population What does random mean? ️️Random means that every member of a population has an equal chance of being chosen What is bias? ️️Prejudice for or against one group or opinion or result in a way that is 'unfair' Describe how to take a random sample of 50 from 1000 pupils in a school ️️Give every pupil pupil a unique number using the school register. Use a random number generator to select 50 random pupil numbers Why do we use stratified sampling? ️️Stratified sampling ensures each group in a population is represented in proportion to its size What is a hypothesis? ️️A hypothesis is an idea or opinion that you start with, and which you test using statistical techniques e.g. "Gromow makes plants grow taller" What is qualitative data? ️️Qualitative data relates to the qualities of something e.g. colour, texture, style, name What is quantitative data? ️️Quantitative data is data that is numerical either counted or measured What is discrete data? ️️Discrete data can only take certain values. It is usually counted data (such as how many people...) but can also be other types e.g. shoe size, clothing sizes What is continuous data? ️️Continuous data is measured data such as distance, weight, time or speed What are the three main methods of collecting data? ️️The three main methods of collecting data are: • Experiment • Observation • Questionnaire What is a pilot survey or pilot study? ️️A pilot survey is a small scale study before a full-scale study is done. Use it to check if your questionnaire or survey 'works', and to fine tune your method/questions What is a leading question? ️️A leading question is one where there is a suggestion that one response is 'better' than another e.g. 'Don't you agree that...' Why would a telephone survey not give a 'fair' sample? ️️Not everyone owns a telephone so not everyone has an equal chance of being contacted Give an advantage of using a face-to-face interview for a questionnaire ️️For example: • more detailed follow up questions are possible • more likely to get an 'honest' response • can explain what questions mean more fully How can you improve the response rate to a postal questionnaire? ️️For example: • reward or prize draw • provide a return envelope • use 'freepost' • offer to collect What is the mode of a set of data? ️️The mode/modal group = what occurs most often • in a bar chart, look for the highest bar • in a frequency polygon, look for the highest peak What is the median of a set of data? ️️The median is the middle value when the data is in order. On a box plot, the median is the line in the middle of the box What is the mean from a list of data? ️️The mean from a list of data is the total of the values divided by how many values there are How do you plot a frequency polygon? ️️On a frequency polygon, plot the frequency on the (vertical axis) against the mid-point of the interval (on the horizontal axis) How do you plot a cumulative frequency polygon? ️️Plot the cumulative frequency (vertical axis) against the upper interval of the group (horizontal axis) When comparing two sets of data, what two factors should you always include? ️️When comparing always include an average (mean, median or mode) and a measure of variation (range or IQR)