Chapter 1 Flashcards
What is a population in statistics?
A population is the whole set of items that are of interest.
What is a census?
A census observes or measures every member of a population.
What is a sample?
A sample is a selection of observations taken from a subset of the population which is used to find out information about the population as a whole.
What is a sampling unit?
Individual units of a population are known as sampling units.
What is a sampling frame?
Sampling units of a population are individually named or numbered to form a sampling frame.
What is a simple random sample?
A simple random sample of size
𝑛
n is one where every sample of size
𝑛
n has an equal chance of being selected.
What is systematic sampling?
In systematic sampling, the required elements are chosen at regular intervals from an ordered list.
What is stratified sampling?
In stratified sampling, the population is divided into mutually exclusive strata (e.g., males and females), and a random sample is taken from each.
What is quota sampling?
In quota sampling, an interviewer or researcher selects a sample that reflects the characteristics of the whole population.
What is opportunity sampling?
Opportunity sampling consists of taking the sample from people who are available at the time the study is carried out and who fit the criteria you are looking for.
What are quantitative variables?
Variables or data associated with numerical observations are called quantitative variables or quantitative data.
What are qualitative variables?
Variables or data associated with non-numerical observations are called qualitative variables or qualitative data.
What is a continuous variable?
A variable that can take any value in a given range is a continuous variable. (e.g., temperature, windspeed).
What is a discrete variable?
A variable that can take only specific values in a given range is a discrete variable. (e.g., number of days with rain).
What is a class in grouped data?
When data is presented in a grouped frequency table, the specific data values are not shown. The groups are more commonly known as classes.
What are class boundaries?
Class boundaries tell you the maximum and minimum values that belong in each class
What is the midpoint of a class?
The midpoint is the average of the class boundaries.
What data is included in the large data set?
The large data set contains data for a number of different variables at eight weather stations.
What variables are recorded in the large data set?
Daily mean temperature (°C)
Daily total rainfall (mm)
Daily total sunshine (hours)
Daily mean wind direction and windspeed (knots)
Daily maximum gust (knots)
Daily maximum relative humidity (%)
Daily mean cloud cover (oktas)
Daily mean visibility (Dm)
Daily mean pressure (hPa)
What is recorded as ‘tr’ in daily total rainfall?
‘tr’ (trace) means an amount less than 0.05 mm.
What is the Beaufort scale used for in the large data set?
The Beaufort scale is used to categorise wind speed.
Calm (0) = Less than 1 knot
Light (1–3) = 1–10 knots
Moderate (4) = 11–16 knots
Fresh (5) = 17–21 knots
What is a knot (kn)?
1 knot = 1.15 mph.
What are oktas?
Oktas measure cloud cover in eighths of the sky covered by clouds.
What is daily mean pressure measured in?
Daily mean pressure is measured in hectopascals (hPa).
Why is familiarity with the large data set important?
You may need to recall trends from within the large data set or identify a location based on given data.
Give one advantage and one disadvantage of a systematic sample
✅ Advantage: Simple & quick for large datasets.
❌ Disadvantage: Can introduce bias if data is arranged in a patterned order.
Give one advantage and one disadvantage of a quota sample
✅ Advantage: Ensures a representative selection based on characteristics.
❌ Disadvantage: Can introduce interviewer bias.
Why might a systematic sample be used for analysis?
It ensures even coverage across the dataset (e.g., selecting every 5th data entry).
Why is it important to understand limitations of the large data set?
Some values may be missing → Not all data is available.
Not representative of all weather conditions → Only covers certain locations & time periods.
Rounded data → Some values (e.g., sunshine, temperature) may be approximated.
Give one advantage and one disadvantage of opportunity sampling.
✅ Advantage: Easy & inexpensive to carry out.
❌ Disadvantage: Unlikely to be representative of the population
Give one advantage and one disadvantage of quota sampling
✅ Advantage: No sampling frame needed, quick and cost-effective.
❌ Disadvantage: Can introduce bias if the interviewer makes subjective decisions.
How does opportunity sampling work?
A sample is taken from people available at the time (e.g., the first 20 people outside a supermarket).
What formula is used for stratified sampling?
Numbersampledinstratum=
Numberinpopulation /
Numberinstratum
×Overallsamplesize
How does stratified sampling work?
The population is divided into mutually exclusive groups (strata), and a random sample is taken from each group.
What are the advantages and disadvantages of simple random sampling?
✅ Advantages:
Free of bias
Each sample unit has an equal chance of selection
❌ Disadvantages:
Not suitable for large populations
Time-consuming if sample size is large
What are the two ways to select numbers for a simple random sample?
1️⃣ Random number generator (calculator, computer, or number table).
2️⃣ Lottery method (write names on tickets and draw from a hat).
How does simple random sampling work?
Every sample of size n has an equal chance of selection
What are the three types of random sampling?
1️⃣ Simple Random Sampling
2️⃣ Systematic Sampling
3️⃣ Stratified Sampling
Give one advantage and one disadvantage of using a sample.
✅ Advantage: Quicker & cheaper than a census.
❌ Disadvantage: Data may not be as accurate, especially if the sample is too small.
Give one advantage and one disadvantage of a census.
✅ Advantage: Should give a completely accurate result.
❌ Disadvantage: Time-consuming and expensive, especially for large populations.
