Unit 4B: Unit 4B: Geographical Geographical Issues Evaluation Issues Evaluation Paper Paper Aim: To explore the pre-release paper Aim: To explore the pre-release paper in more depth with a focus on fieldwork in more depth with a focus on fieldwork and case studies. and case studies. Objectives: To understand sampling, Objectives: To understand sampling, fieldwork techniques and some case fieldwork techniques and some case studies from the dft website. studies from the dft website.
Transcript
Unit 4B: Geographical Unit 4B: Geographical Issues Evaluation PaperIssues Evaluation Paper
Aim: To explore the pre-release paper in more Aim: To explore the pre-release paper in more depth with a focus on fieldwork and case depth with a focus on fieldwork and case
studies.studies.
Objectives: To understand sampling, fieldwork Objectives: To understand sampling, fieldwork techniques and some case studies from the dft techniques and some case studies from the dft
1.1. What are the disadvantages of roads?What are the disadvantages of roads?2.2. Why do people want to get back to Why do people want to get back to
walking and cycling?walking and cycling?3.3. What does Sustrans mean?What does Sustrans mean?4.4. What are the aims of sustrans?What are the aims of sustrans?5.5. How many connect 2 bids are there?How many connect 2 bids are there?6.6. What is the problem with What is the problem with
Cardiff/Glasgow/Hastings-Bexhill?Cardiff/Glasgow/Hastings-Bexhill?7.7. What is the solution to the problem in What is the solution to the problem in
Cardiff/Glasgow/Hastings-Bexhill?Cardiff/Glasgow/Hastings-Bexhill?8.8. What are the benefits to having a bridge What are the benefits to having a bridge
over the River Tey and Southwark?over the River Tey and Southwark?
Let’s hear from you…Let’s hear from you…
Each group is going to present a Each group is going to present a fieldwork method. For each method fieldwork method. For each method explain the advantages and explain the advantages and disadvantages.disadvantages.
What is sampling?What is sampling?A ‘short-cut' method for investigating a whole population A ‘short-cut' method for investigating a whole population Data is gathered on a small part of the whole ‘parent population' Data is gathered on a small part of the whole ‘parent population' or ‘sampling frame' and used to inform what the whole picture is or ‘sampling frame' and used to inform what the whole picture is likelike
Why sample?Why sample? In reality there is simply not enough:In reality there is simply not enough:Time Time Energy Energy Money Money Labour / man power Labour / man power Equipment Equipment Access to suitable sitesAccess to suitable sitesto measure every single ‘item' or site within the ‘parent population' to measure every single ‘item' or site within the ‘parent population'
or whole ‘sampling frame'or whole ‘sampling frame'Therefore an appropriate sampling strategy is adopted to obtain a Therefore an appropriate sampling strategy is adopted to obtain a
representative, and statistically valid sample of the whole.representative, and statistically valid sample of the whole.
Sampling considerationsSampling considerations
Larger sample sizes are more accurate representations of the Larger sample sizes are more accurate representations of the wholewhole
The sample size chosen is a balance between obtaining a The sample size chosen is a balance between obtaining a statistically valid representation, and the time, energy, money, statistically valid representation, and the time, energy, money, labour, equipment and access available. labour, equipment and access available.
A sampling strategy made with the minimum of bias is the most A sampling strategy made with the minimum of bias is the most statistically valid. statistically valid.
Most approaches assume that the parent population has a ‘normal Most approaches assume that the parent population has a ‘normal distribution' where most items or individuals clustered close to the distribution' where most items or individuals clustered close to the mean, with few extremes. mean, with few extremes.
A 95% probability or confidence level is usually assumed, e.g. 95% A 95% probability or confidence level is usually assumed, e.g. 95% of items or individuals will be within + or - 2 standard deviations of items or individuals will be within + or - 2 standard deviations from the mean (see graph) from the mean (see graph) This also means that up to 5% may lie outside of this - sampling, This also means that up to 5% may lie outside of this - sampling, no matter how good can only ever be claimed to be a very close no matter how good can only ever be claimed to be a very close estimate.estimate.
Sampling techniquesSampling techniques
Three main types of sampling strategy:Three main types of sampling strategy:Random Random Systematic Systematic StratifiedStratified
Within these types, you may then decide on a:Within these types, you may then decide on a:a) Point a) Point b) Lineb) Linec) Areac) Areamethod.method.
Random samplingRandom sampling
Least biased of all sampling techniques: there is no subjectivity - Least biased of all sampling techniques: there is no subjectivity - each member of the total population has an equal chance of being each member of the total population has an equal chance of being selected selected
Can be obtained using random number tables Can be obtained using random number tables
Microsoft Excel has a function to produce random number; Microsoft Excel has a function to produce random number; The function is simply The function is simply =RAND() =RAND() Type that into a cell and it will produce a random number in that Type that into a cell and it will produce a random number in that cell. Copy the formula throughout a selection of cells and it will cell. Copy the formula throughout a selection of cells and it will produce random numbers. produce random numbers. You can modify the formula to obtain whatever range you wish, You can modify the formula to obtain whatever range you wish, e.g. if you wanted random numbers from 1 to 250, you could enter e.g. if you wanted random numbers from 1 to 250, you could enter the following formula: the following formula: =INT(250*RAND())+1 =INT(250*RAND())+1 Where: INT eliminates the digits after the decimal, 250* creates Where: INT eliminates the digits after the decimal, 250* creates the range to be covered, and +1 sets the lowest number in the the range to be covered, and +1 sets the lowest number in the range. range. Paired numbers could also be obtained using;Paired numbers could also be obtained using;=INT(9000*RAND())+1000=INT(9000*RAND())+1000These can then be used as grid coordinates, metre and centimetre These can then be used as grid coordinates, metre and centimetre sampling ‘stations' along a transect, or in any feasible way!sampling ‘stations' along a transect, or in any feasible way!
MethodologyMethodologyA. Random point samplingA. Random point sampling
A grid is drawn over a map of the A grid is drawn over a map of the study area study area Random number tables are used Random number tables are used to obtain coordinates / grid to obtain coordinates / grid references for the points references for the points Sampling takes place as feasibly Sampling takes place as feasibly close to these points as possibleclose to these points as possible
B. Random line samplingB. Random line samplingPairs of coordinates or grid Pairs of coordinates or grid references are obtained using references are obtained using random number tables, and random number tables, and marked on a map of the study marked on a map of the study area area These are joined to form lines to These are joined to form lines to be sampledbe sampled
C. Random area samplingC. Random area samplingRandom number tables generate Random number tables generate coordinates or grid references coordinates or grid references which are used to mark the which are used to mark the bottom left (south west) corner of bottom left (south west) corner of quadrats or grid squares to be quadrats or grid squares to be sampledsampled
Advantages and disadvantages Advantages and disadvantages of random samplingof random sampling
Advantages:Advantages:Can be used with large sample populations. Can be used with large sample populations. Avoids bias.Avoids bias.
Disadvantages:Disadvantages:Can lead to poor representation of the overall ‘parent' Can lead to poor representation of the overall ‘parent' population or area if large areas are not ‘hit' by the random population or area if large areas are not ‘hit' by the random numbers generated. This is made worse if the study area is numbers generated. This is made worse if the study area is very large. very large.
There may be practical constraints in terms of time There may be practical constraints in terms of time available and access to certain parts of the study area.available and access to certain parts of the study area.
Systematic samplingSystematic sampling
Samples are chosen in a systematic, or regular way.Samples are chosen in a systematic, or regular way.
They are evenly / regularly distributed in a spatial context, They are evenly / regularly distributed in a spatial context, e.g. every 2 metres along a transect line. e.g. every 2 metres along a transect line.
They can be at equal / regular intervals in a temporalThey can be at equal / regular intervals in a temporalcontext, e.g. every half hour or at set times of thecontext, e.g. every half hour or at set times of theday. day.
They can be regularly ‘numbered', e.g. every 10th house orThey can be regularly ‘numbered', e.g. every 10th house orperson.person.
MethodologyMethodologyA.A. Systematic point samplingSystematic point sampling
A grid can be used and the points can be at A grid can be used and the points can be at the intersections of the grid lines (A), or in the intersections of the grid lines (A), or in the middle of each grid square (B). the middle of each grid square (B). Sampling is done at the nearest feasible Sampling is done at the nearest feasible place. Along a transect line, sampling points place. Along a transect line, sampling points for vegetation / pebble data collection could for vegetation / pebble data collection could be identified systematically, e.g. every 2 be identified systematically, e.g. every 2 metres or every 10th pebble metres or every 10th pebble
B. Systematic line samplingB. Systematic line samplingThe ‘eastings' or ‘northings' of the grid on a The ‘eastings' or ‘northings' of the grid on a map can be used to identify transect lines map can be used to identify transect lines (C and D) Alternatively, along a beach it (C and D) Alternatively, along a beach it could be decided that a transect up the could be decided that a transect up the beach will be conducted every 20 metres beach will be conducted every 20 metres along the length of the beachalong the length of the beach
C. Systematic area samplingC. Systematic area samplingA ‘pattern' of grid squares to be sampled A ‘pattern' of grid squares to be sampled can be identified using a map of the study can be identified using a map of the study area, e.g. every 2nd / 3rd grid square down area, e.g. every 2nd / 3rd grid square down or across the area (E) - the south west or across the area (E) - the south west corner will then mark the corner of a corner will then mark the corner of a quadrat. Patterns can be any shape or quadrat. Patterns can be any shape or direction as long as they are regular (F)direction as long as they are regular (F)
Advantages and disadvantages Advantages and disadvantages of systematic samplingof systematic sampling
Advantages:Advantages:It is more straight-forward than random sampling. It is more straight-forward than random sampling. A grid doesn't necessarily have to be used - sampling just A grid doesn't necessarily have to be used - sampling just has to be at uniform intervals. has to be at uniform intervals. A good coverage of the study area can be more easily A good coverage of the study area can be more easily achieved than using random sampling.achieved than using random sampling.
Disadvantages:Disadvantages:It is more biased, as not all members or points have an It is more biased, as not all members or points have an equal chance of being selected. equal chance of being selected. It may therefore lead to over - or under - representation of It may therefore lead to over - or under - representation of a particular pattern.a particular pattern.
Stratified samplingStratified sampling
This method is used when the parent This method is used when the parent population or sampling frame is made up population or sampling frame is made up of sub-sets of known size. These sub-sets of sub-sets of known size. These sub-sets make up different proportions of the total, make up different proportions of the total, and therefore sampling should be and therefore sampling should be stratified to ensure that results are stratified to ensure that results are proportional and representative of the proportional and representative of the whole.whole.
The population can be divided into known groups, The population can be divided into known groups, and each group sampled using a systematic and each group sampled using a systematic approach. The number sampled in each group approach. The number sampled in each group should be in proportion to its known size in the should be in proportion to its known size in the parent population.parent population.
For example: the make-up of different social For example: the make-up of different social groups in the population of a town can be groups in the population of a town can be obtained, and then the number of questionnaires obtained, and then the number of questionnaires carried out in different parts of the town can be carried out in different parts of the town can be stratified in line with this information. A stratified in line with this information. A systematic approach can still be used by asking systematic approach can still be used by asking every 5th person. every 5th person.
Stratified random samplingStratified random sampling
A wide range of data and fieldwork situations can lend A wide range of data and fieldwork situations can lend themselves to this approach - wherever there are two study themselves to this approach - wherever there are two study areas being compared, e.g. two woodlands, river areas being compared, e.g. two woodlands, river catchments, rock types or a population with sub-sets of catchments, rock types or a population with sub-sets of known size, e.g. woodland with distinctly different habitats known size, e.g. woodland with distinctly different habitats Random point, line or area techniques can be used as long Random point, line or area techniques can be used as long as the number of measurements taken is in proportion to as the number of measurements taken is in proportion to the size of the whole.the size of the whole.For example: if an area of woodland was the study site, For example: if an area of woodland was the study site, there would likely be different types of habitat (sub-sets) there would likely be different types of habitat (sub-sets) within it. Random sampling may altogether ‘miss' one or within it. Random sampling may altogether ‘miss' one or more of these. Stratified sampling would take into account more of these. Stratified sampling would take into account the proportional area of each habitat type within the the proportional area of each habitat type within the woodland and then each could be sampled accordingly; if woodland and then each could be sampled accordingly; if 20 samples were to be taken in the woodland as a whole, 20 samples were to be taken in the woodland as a whole, and it was found that a shrubby clearing accounted for 10% and it was found that a shrubby clearing accounted for 10% of the total area, 2 samples would need to be taken within of the total area, 2 samples would need to be taken within the clearing. The sample points could still be identified the clearing. The sample points could still be identified randomly (A) or systematically (B) within each separate randomly (A) or systematically (B) within each separate area of woodland.area of woodland.
Stratified random samplingStratified random sampling
Advantages and disadvantages Advantages and disadvantages of stratified samplingof stratified sampling
Advantages:Advantages:It can be used with random or systematic sampling, and with It can be used with random or systematic sampling, and with point, line or area techniques. point, line or area techniques. If the proportions of the sub-sets are known, it can generate If the proportions of the sub-sets are known, it can generate results which are more representative of the whole population. results which are more representative of the whole population. It is very flexible and applicable to many geographical enquiries. It is very flexible and applicable to many geographical enquiries. Correlations and comparisons can be made between sub-sets.Correlations and comparisons can be made between sub-sets.
Disadvantages:Disadvantages:The proportions of the sub-sets must be known and accurate if it is The proportions of the sub-sets must be known and accurate if it is to work properly. to work properly. It can be hard to stratify questionnaire data collection - accurate, It can be hard to stratify questionnaire data collection - accurate, up to date population data may not be available and it may be up to date population data may not be available and it may be hard to identify people's age or social background effectively.hard to identify people's age or social background effectively.
Now some work on the example Now some work on the example case studies: Link Schoolscase studies: Link Schools
For the case study you have been For the case study you have been given explain the key points of the given explain the key points of the scheme. This may include scheme. This may include background, aims/objectives, background, aims/objectives, advantages and you may have some advantages and you may have some disadvantages.disadvantages.
Over the holiday you must review your Over the holiday you must review your booklet. Create some revision notes. Go booklet. Create some revision notes. Go through all the work we have covered and through all the work we have covered and look at the websites mentioned in the look at the websites mentioned in the booklet.booklet.
Remember: you are going to have to Remember: you are going to have to make a make a justifiedjustified decision about a situation decision about a situation posed by the examiner. You will asked posed by the examiner. You will asked long and short answer questions.long and short answer questions.
