1.1
What is a census and what are some of its advantages and disadvantages?
A census observes or measures every member of the population.
+It should give a completely accurate result.
-Time consuming and expensive.
-Hard to process large quantities of data.
-Can’t be used when the testing process destroys the item.
1.1
What is a sample and what are its advantages and disadvantages?
A sample is a selection from a subset of the whole population that is used to find out information about the population as a whole.
+Fewer people have to respond.
+Less time consuming and expensive than a census.
-The data may not be accurate.
-The sample may not be large enough to give accurate information about the whole population.
1.1
What is a sampling frame?
It is created when the sampling units of a population are individually named or numbered.
1.2
What are the different methods of random sampling and how do they work?
•Simple random sampling - a sample of size n where every sample size n has an equal chance of being selected.
•Systematic sampling - the required elements are chosen at regular intervals from an ordered list.
•Stratified sampling - the population is divided into mutually exclusive strata (e.g. males and females) and a random sample is taken from each.
1.2
What are some advantages and disadvantages of simple random sampling?
+Free of bias.
+Easy and cheap to implement for small populations/samples.
+Each sampling unit has a known and equal chance of selection.
-A sampling frame is needed.
-Not suitable for large populations/samples.
1.2
What are some advantages and disadvantages of systematic sampling?
+Simple and quick to use.
+Suitable for large samples/populations.
-A sampling frame is needed.
-It can introduce bias if the sampling frame isn’t random.
1.2
What are some advantages and disadvantages of stratified sampling?
+Sample accurately reflects the population structure.
+Guarantees proportional representation of groups within a population.
-Population must be clearly classified into distinct strata.
-Selection from each strata has the same issues as simple random sampling.
1.3
What are the methods of non-random sampling and how do they work?
•Quota sampling - an interviewer/researcher selects a sample that reflects the characteristics of the whole population.
•Opportunity sampling - consists of taking a sample from people who are available at the time the study is carried out and who fit the required criteria.
1.3
What are some advantages and disadvantages of quota sampling?
+No sampling frame required.
+Quick, easy and inexpensive.
+Allows for easy comparison between different groups within a population.
-Can introduce bias.
-Non-responses aren’t recorded.
-Population must be divided into groups, which can be costly or inaccurate.
1.3
What are some advantages and disadvantages of opportunity sampling?
+Easy to carry out.
+Inexpensive.
-Unlikely to provide a representative sample.
-Highly dependent on individual researcher.
1.4
What are continuous and discrete variables and how are they different?
•Continuous variables can take any values in a given range (e.g. 2s, 2.11s).
•Discrete variables can only take specific values in a given range(e.g. 1 girl, 2 boys).
1.4
What are some important aspects of grouped frequency tables?
•The groups are commonly known as classes.
•The midpoint is the average of the class boundaries.
•The class width is the difference between the upper and lower class boundaries.
1.5
In terms of the large data set what is the Daily Mean Temperature and how is it recorded?
•Measured in °C.
•The average temperature readings in a 24 hour period.
1.5
In terms of the large data set what is the Daily Total Rainfall and how is it recorded?
•Measured in millimetres(mm).
•Amounts less than 0.05mm are recorded as ‘tr.’ or ‘trace’.
1.5
In terms of the large data set what is the Daily Total Sunshine and how is it recorded?
•Measured to the nearest tenth of an hour.
1.5
In terms of the large data set what is the Daily Mean wind Direction and Speed and how is it recorded?
•Recorded in knots, averaged over 24 hours from midnight to midnight, at 10 metres above ground.
•Knot (kn) is a ‘nautical mile per hour’ 1kn = 1.15mph
•Windspeed is also categorised on the Beaufort scale:
0 - Calm (<1kn).
1-3 - Light (1-10kn).
4 - Moderate (11-16kn).
5 - Fresh (17-21kn).
1.5
In terms of the large data set what is the Daily Maximum Gust and how is it recorded?
•Measured in knots.
•The highest instantaneous windspeed recorded.
•Also records the direction from which the gust came from.
1.5
In terms of the large data set what is the Daily Maximum Relative Humidity and how is it recorded?
•Given as a percentage of air saturation with water vapour.
•>95% give rise to mist and fog.
1.5
In terms of the large data set what is the Daily Mean Cloud Cover and how is it recorded?
•Measured in ‘oktas’ or eights of the sky covered by cloud.
1.5
In terms of the large data set what is the Daily Mean Visibility and how is it recorded?
•Measured in decameteres (Dm).
•This is the greatest horizontal distance at which an object can be seen in daylight.
1.5
In terms of the large data set what is the Daily Mean Pressure and how is it recorded?
•Measured in hectopascals (hPa).
