Dale Fort Blog Number 41

3 04 2015

Crowded Coasts

St Davids is the smallest city in the UK.  It has had a Christian presence for more than 1400 years, since St David founded his religious order there in the 6th Century.  You can find out all about St David and his chum Elvis in Blog Number 13

https://dalefort.wordpress.com/2012/12/10/dale-fort-blog-number-13/

Before you do that, why not join Dale Fort Tutor Kim Houkes and her  charges as they investigate the impacts of tourism around the area?

Don’t miss the next blog.  Could it be another geography film?





Dale Fort Blog Contents 1 – 45

3 04 2015

Dale Fort Blog Contents

Number 1

All about nematodes

https://dalefort.wordpress.com/2012/03/

Number 2

3 You Tube clips:

Starlings at Mabesgate

Error Bars in Excel 2007

Measuring Heights on Seashores

https://dalefort.wordpress.com/2012/04/02/dale-fort-blog-number-2/

Number 3

The History of Dale Fort part 1 (all about the rocks)

https://dalefort.wordpress.com/2012/04/03/dale-fort-blog-number-3/

Number 4

The History of Dale Fort part 2  (the construction  materials of Dale Fort).  Far more exciting than it sounds, you won’t want to miss it, go there NOW

https://dalefort.wordpress.com/2012/04/18/dale-fort-blog-number-4/

Number 5

Sargassum muticum in Britain (with a video on how it makes babies)

https://dalefort.wordpress.com/2012/04/25/dale-fort-blog-number-5/

Number 6

The History of Dale Fort part 3, The First Humans

https://dalefort.wordpress.com/2012/04/

Number 7

Silverfish and their ways

https://dalefort.wordpress.com/2012/05/10/dale-fort-blog-number-7/

Number 8

The fat-bellied book chewer

https://dalefort.wordpress.com/2012/05/

Number 9

Seaweed research at Dale Fort

https://dalefort.wordpress.com/2012/07/

Number 10

Wormhole research at Dale Fort

https://dalefort.wordpress.com/2012/08/07/dale-fort-blog-number-10/

Number 11

Limpets and their mysterious ways

https://dalefort.wordpress.com/2012/08/27/dale-fort-blog-number-11/

Number 12

Anne, Bridget, Cadoc and David

https://dalefort.wordpress.com/2012/12/07/dale-fort-blog-number-12/

Number 13

St David and his friend Elvis

https://dalefort.wordpress.com/2012/12/10/dale-fort-blog-number-13/

Number 14

Dancing bananas:  Just how many are there?

https://dalefort.wordpress.com/2013/01/16/dale-fort-blog-number-14/

Number 15

Six-legged female vampires

https://dalefort.wordpress.com/2013/01/23/dale-fort-blog-number-15/

Number 16

Cry Havoc!  And let loose the dogs of accountancy………The History of Dale Fort part 6

https://dalefort.wordpress.com/2013/04/22/dale-fort-blog-number-16/

Number 17

Wee timorous beasties

https://dalefort.wordpress.com/2013/04/30/dale-fort-blog-number-17/

Number 18

A magical island where strange events take place

https://dalefort.wordpress.com/2013/07/02/dale-fort-blog-number-18/

 Number 19

The many faces of the mean (and by the way Bill, smoking is neither big nor clever)

https://dalefort.wordpress.com/2013/10/11/dale-fort-blog-number-19/

Number 20

Deviant Beards and other exciting topics

https://dalefort.wordpress.com/2013/10/11/dale-fort-blog-number-20/

Number 21

Welsh in 10 Minutes (ddim yn rhugl)

https://dalefort.wordpress.com/2013/10/24/dale-fort-blog-number-21/

Number 22

Halloween Special.  Read it with the light on……..

https://dalefort.wordpress.com/2013/10/25/dale-fort-blog-number-22/

Number 23

Back to matters more prosaic but useful I hope.  How to get a quick frequency distribution histogram out of Excel 2007

https://dalefort.wordpress.com/2013/11/06/dale-fort-blog-number-23/

Number 24

Spectacular weather, huge waves, the demise of a bridge, the scaring of a photographer and much more

https://dalefort.wordpress.com/2014/01/08/dale-fort-blog-number-24/

Number 25

BARNACLES  so much more than just the worst part of a keel-hauling

https://dalefort.wordpress.com/2014/01/10/dale-fort-blog-number-25/

Number 26

NUNZILLA makes her debut:  She knows about seaweeds, she’s a nun, she’s clockwork, she breaths fire.   What more could you want?  More history, that’s what and you’ll get it in Blog 26

https://dalefort.wordpress.com/2014/02/18/dale-fort-blog-number-26/

Number 27

TARDIGRADES…….No it’s not a Norwegian swearword.  Their common name is water bears and they are astonishing creatures.  Read about them and then construct your own with our free build your own tardigrade kit.  Ordvykejys….now that’s a Norwegian swear word.

https://dalefort.wordpress.com/2014/02/21/dale-fort-blog-number-27/

Number 28

House Dust Mites…..I realise that it would be hard to top the spacetastic subjects of the previous blog but house dust mites are still extremely interesting creatures that eat human flesh and give you allergies.  Read all about them here.

https://dalefort.wordpress.com/2014/03/07/dale-fort-blog-number-28/

Number 29

WOODWORM All you could wish to know and probably more about about the unsung heroes of the Anti-Furniture League

https://dalefort.wordpress.com/2014/03/11/dale-fort-blog-number-29/

Number 30

Spider Blog,  Spider Blog,   Does whatever a Spider Blog does…..

https://dalefort.wordpress.com/2014/03/14/dale-fort-blog-number-30/

Number 31

The History of Dale Fort Part the Eighth.  200 years in 1200 words, suitable for home freezing.

https://dalefort.wordpress.com/2014/04/07/dale-fort-blog-number-31/

Number 32

Red and yellow and not pink and green, orange and not purple and blue……..seaweeds and light

https://dalefort.wordpress.com/2014/04/08/dale-fort-blog-number-32/

Number 33

Rocky shore monitoring at Dale Fort Part 1.  Channelled wrack and rough winkles have rarely been given so much attention and for so long.

https://dalefort.wordpress.com/2014/06/12/dale-fort-blog-number-33/

Number 34

Rocky shore monitoring at Dale Fort Part 2.  Species diversity, small winkles, limpets, barnacles and purple topshells.  Possibly more than you ever thought you wanted to know about these fascinating creatures

https://dalefort.wordpress.com/2014/09/04/dale-fort-blog-number-33-2/

Number 35

The History of Dale Fort Part the Ninth:  Charles Louis Napoleon,  80 cigarettes a day,  The Ladies of Royal Ballet, Beating up Chartists, Emperor of France, Kidnapper of vultures, World Ping-Pong Champion 1846 (OK I made the last one up)…what a guy…

https://dalefort.wordpress.com/2014/09/04/dale-fort-blog-number-35/

Number 36

STATS for TWITS.                                                                                                                                                              A simple guide to how hypothesis testing statistics work and some common tests and what they do. Could any blog be more fun than that?   Well yes, actually but I hope you’ll find it useful nonetheless.

https://dalefort.wordpress.com/2014/09/05/dale-fort-blog-number-36/

Number 37

A visit to another magical island (see also Blog Number 18) and some lesser known aspects of its history

https://dalefort.wordpress.com/2014/09/26/dale-fort-blog-number-37/

Number 38

Nadolig Llawen pawb

Merry Christmas Everybody (c N. Holder 1973)

https://dalefort.wordpress.com/2014/12/05/dale-fort-blog-number-38/

Number 39

One of the great things about geography at Dale Fort is that you get to go to some of the  best and most interesting places .  Here we visit The Preseli Mountains to study The Afon Synfynwy (translation: The river who runs back up the slope to the church where the goat is tied to the tree with the wasp’s nest on the 3rd bough from the top by the church with the wobbly pew at the back)

https://dalefort.wordpress.com/wp-admin/post.php?post=528&action=edit&message=6&postpost=v2

Number 40

More geography at Dale Fort.  This one is about rebranding in the interesting town of Milford Haven (Aberdaugleddau, translation:  The lovely town by the sea, very close to Dale Fort, with the llamas that is easily the best place to do urban rebranding).  (You might wish to read the blog and check the veracity of this translation).

https://dalefort.wordpress.com/2015/04/03/dale-fort-blog-number-40/

Number 41

St. Davids is the smallest city in the UK but it’s so interesting and attractive that it gets huge numbers of tourists.  Many of them are pilgrims come to worship at the huge Norman cathedral.  Many come for the ice cream and still more for the beaches and the surfing and the sailing.  What’s wrong with these people?  They should be coming to do Crowded Coasts at Dale Fort.  Dale Fort Tutor Kim Houkes shows us how it’s done.

https://dalefort.wordpress.com/2015/04/03/dale-fort-blog-number-41/

Number 42

Has longshore drift ever been more stimulating?  Possibly not.  Find out for yourself here:

https://dalefort.wordpress.com/2015/04/10/dale-fort-blog-number-42/

Number 43

The wait is over.  Now at last you can find out how Britain responded to Napoleon III’s shenanigans.

https://dalefort.wordpress.com/2015/09/13/dale-fort-blog-number-43/

Number 44

Bill Ballantine.  One of the greats of marine conservation RIP

https://dalefort.wordpress.com/2015/11/03/dale-fort-blog-number-45/

Number 45

Look at the colours man……

https://dalefort.wordpress.com/2015/11/26/dale-fort-blog-number-45-2/





Dale Fort Blog Number 40

3 04 2015

Rebranding at Milford Haven

Join Dale Fort Tutors Martha Boalch, Catherine Gillat as they explore rebranding with some fortunate sixth formers.  Milford Haven (Aberdaugleddau = mouth of the two Cleddaus) has a short but fascinating history beginning as a planned town set up largely by Sir Charles Greville a little over 200 years ago.  The initial plan was to capture the Atlantic shipping trade, lack of rail links and inland communications made that a limited success.  Greville then developed the town as a whaling centre with a community of Quaker whalers from Nantucket.  Their leader was Samuel Starbuck and the Starbucks were important in the early development of the town  To this day you will find more coffee in Milford than anywhere else in Wales (only joking).  The development of coal gas street lighting in London led to a fall in the value of whale oil (it was valued because it burned clean, producing little soot).  The whale oil industry failed.  Railways came and with rapid communication links inland Milford began to develop as the major fishing port in Wales.  Fishing peaked just after World War Two and then began a fairly rapid decline.  The Suez crisis (1956) meant there was a need for a port that could accept huge oil tankers on the west coast of Britain.  Nelson himself had declared Milford Haven as the finest natural harbour in the world and it was deep enough and sheltered enough to accommodate huge oil tankers.  Thus began the rise of the oil industry.  By 1985 there were four oil refineries along the Haven.  The ups and downs of the oil industry have seen this reduce to one by 2015.  However, since North Sea Gas is beginning to run out and the UK has become dependent upon natural gas, yet another new industry has developed.  The most costly project in the history of Wales has seen the building of the new Liquified Natural Gas plant at South Hook on the old Esso refinery site.  This imports LNG (Liquified Natural Gas) from Qatar and is capable of handling up to a third of the UK’s gas requirements.  There are five huge cylindrical tanks to hold the gas, each about the size of The Albert Hall (43m high, 80m or so in diameter).  Milford has an interesting cultural life as well.  Its Torch Theatre being one of the best in Wales.  All in all it’s a very interesting town and you would do well to investigate it for yourselves.  Why not enquire about geography courses at Dale Fort?

The next blog will be another film about geography at Dale Fort.





Dale Fort Blog Number 39

28 03 2015

Geography in The Preseli Mountains

Join Dale Fort’s Catherine Gillatt and her students at the source of Afon Synfynwy in the heart of The Preseli Mountains.  Marvel at how good the weather is.  Be thrilled by the beautiful scenery.  Better still come to Dale Fort and do it for yourselves.

The next blog will feature another film about geography at Dale Fort.





Dale Fort Blog Number 38

5 12 2014

Happy Christmas

from everyone at Dale Fort

 





Dale Fort Blog Number 37

26 09 2014

Dale Fort’s connection with the Pembrokeshire Island of Skokholm

On the 9th of September 2014, my colleague Amy and I were privileged to visit Skokholm in the company of Mark Burton, Kate Locke and Jen Jones of The Skomer Marine Reserve. It has been many years since much attention has been given to the shores of the island and we helped them do some preliminary inspections.

Above the landingcrab coveApproaching the quarry with lighthouseThe Quarry

 

I thought I’d use this as an opportunity to tell you some of the history of the island and a couple of lesser known stories.

The island of Skokholm is about 2 miles offshore and 7 miles from Dale Fort. The name is Old Norse (like its neighbour Skomer) and its meaning is uncertain. Island of Stocks (where ships were built) or Island of Logs are two dodgy-sounding suggestions.

The island has a similar history to neighbouring Skomer having its first historical mentions as a rabbit warren in the 17th Century (rabbits were probably introduced in the 13th Century). In 1940, the government used Skokholm as a site for myxomatosis trials (that’s a story that might appear in another blog).

Skokholm was the UK’s first full-time bird observatory. It is owned by The Wildlife Trust of South and West Wales, having been purchased from Dale Castle Estates in 2006. It has been managed by the trust since 1937. The island was declared a National Nature Reserve in 2008 mainly because of its seabird colonies (Skokholm and Skomer provide nesting sites for at least half of the world’s population of manx shearwaters)

manx shearwater

Our story today starts with a young man called John Fursdon.

John first visited Skokholm in 1938 when he stayed with the Lockley family who had leased the island and were trying to lead a self-sufficient island existence as well as run the observatory. He liked it so much that he returned in 1939 and again in 1940 when he helped the Lockleys move from the island just after the beginning of the War.

After the conflict ended because of his previous experience John was asked to be the first post-war Warden of Skokholm. He took up the post for the 1946 season.

The West Wales Field Society (WWFS) had decided that they needed a mainland base from which to service their Bird Observatory on Skokholm and to promulgate “education and conservation of the unspoiled countryside of West Wales”.

The Honorary Chairman of the WWFS was one of its founder members, ex-Skokholm resident, Ronald Lockley. He persuaded the recently formed Council for the Promotion of Field Studies (CPFS later to become the FSC) that Dale Fort would be an ideal location for a maritime field centre, with the added bonus of an intimate association with the island of Skokholm.

The WWFS agreed to buy and set up the fort as a field centre if the CPFS agreed to guarantee the financial liability for staffing and maintenance of the fort as a Field Centre. The WWFS then set up an appeal for £10,000 to enable them to purchase the fort and 20 acres of surrounding land.

Appeal leaflet 1946

After protracted negotiations complicated by the fact that the owner was resident in Switzerland; Mrs. Lee-Roberts finally accepted £6000 from The West Wales Field Society for the purchase of Dale Fort. On 15th February 1947 the WWFS signed their half of the contract for the transaction.

Even before Mrs Lee Roberts had signed her half of the contract, her solicitors gave permission for the WWFS to occupy the site and begin the conversion of the buildings. The first man there was John Fursdon, who effectively was the first person in charge at the new field centre. He spent many hours cleaning up the mess left by the military who had occupied the site during the war.

John F with caption   I met John when he visited Dale Fort in 2003, (he died in 2011 aged 91). He had a wealth of amusing stories and was a thoroughly sound egg. Remembering his days on Skokholm, he told me about an unusual problem experienced by Trinity House staff when they attempted to supply the Skokholm Lighthouse.

The lighthouse builders had installed a railway track that led from the landing stage right across the island 1500 metres or so, to the site of the lighthouse on the extreme westerly point. The railway was used to transport building materials to the site.

Skokholm with railway route

After the building was completed the railway was still used to transport supplies and equipment. The stuff would be swung ashore using the large derricks near the landing stage and be loaded into a railway wagon.

There was no mechanical engine, the motive force was provided by a donkey who most of the time was free to wander about the island ad lib. It was an intelligent animal and it soon learned to recognize the sound of the supply vessel while it was still way out at sea and undetected by humans. Before the boat neared the island the donkey would take itself off to the Pond and go and stand in the middle, thus rendering herself unavailable for wagon-hauling. The animal then had to be enticed back onto to dry land in the traditional manner using a carrot on a stick.

John kindly sent me copies of some of his films based on the wildlife of the islands. The first part of his 1948 Pembrokeshire Wildlife film concerning Skokholm, with his own commentary (added I think when he transferred the film to videotape) can be seen here:

https://www.youtube.com/watch?v=A6sUsNax6WQ&feature=youtu.be

John’s time in charge at Dale Fort was soon to come to an end. In March 1947 an advertisement appeared in The Times from The Council for the Promotion of Field Studies. Assistant Wardens were required for Dale Fort, Flatford Mill and Malham Tarn. Wing Commander J.H. Barrett and several other candidates were interviewed for the posts on 15th April 1947 and John Barrett became the first Council for the Promotion of Field Studies Warden of Dale Fort Field Centre. On 1st July 1947 John and Ruth Barrett and their two children moved to Dale

From The Western Telegraph and Cymric Times 24th July 1947:

DALE FORT AS A NATURE CENTRE.

£10,000 purchase by West Wales Field Society

Dale Fort with 20 acres of land has been acquired by the West Wales Field Society as a nature centre. It will accommodate 50 students. For the purpose the society requires £10,000. Provided this sum is secured, financial liability for the staffing and management of the Fort as a Field Centre is guaranteed by the Council for the Promotion of Field Studies, which is receiving a grant for that purpose from the Ministry of Education. The CPFS will develop Dale Fort.

The £10,000 is needed to help develop Dale Fort and to pay the expenses of a secretary in conducting the appeal. Any balance will go towards the creation of further field centres and nature reserves.

Mr. R.M. Lockley, the chairman referred to the matter at the annual meeting of the Field Society last Thursday when he said that Skokholm had been established as a Bird Observatory while at Dale Fort they would have a centre for cultural outdoor research of great importance. He thought with energy, practice and forethought they would secure the £10,000.

Mr. John Fursdon said he would like to see the formation of a group or sub-organization to stimulate by means of rambles, lectures, film shows and instruction by experienced naturalists an interest in the locality in birds and wildlife. They had few records of bird life in the interior. They had a good season at Skokholm which had been filled to capacity, although the number of day visitors was limited through the society not having their own boat. They had ringed 2000 birds last year. Naturalists from Sweden and Switzerland were amongst the foreign visitors.

Mr. John Barrett, a former RAF Wing Commander, who has undertaken the duties of Warden at Dale Fort was introduced to the members. He said that the CPFS and the Field Society, working together, could accomplish something very important, something that would be the envy of the world.

Dale Fort was to be the mainland base for visitors to Skokholm from 1947 to 1965. This was a major part of the field centre’s original raison d’etre. Weather permitting, every Thursday an early morning boat would leave Dale Fort Jetty to take new visitors and remove the old ones from the island. Years later (1998), Ruth Barrett’s abiding memory of Skokholm was the ridiculously early start required on Skokholm days. Recently, (11.09.14), Dale Fort was privileged to be visited by Mr and Mrs Barry Page. (Barry was Deputy Warden and Mrs Page was the Bursar in the early 1960s). One of Mr Page’s abiding memories also concerned Skokholm, because he had to get up even earlier on Thursdays and drive to Milford Station to meet the 0430 train to collect the next set of visitors to the island.

In 1969 the lease on Skokholm Island ran out.  Hugh Lloyd-Philips of Dale Castle who owned the island renewed the lease for the West Wales Naturalist Trust (ex-WWFS) but was not happy about the continued involvement of the Field Studies Council. There had been an almighty row over a bungalow, which had been built on the island early in 1967. The island’s owner had not given permission for this erection. The Field Studies Council didn’t think they needed his permission and put it up anyway. It turned out that Lloyd-Philips was right and he insisted that it be pulled down. This was duly done by (much to their amazement) the same builders who had just, with extreme difficulty, put it up. David Stanbury, a regular visitor to the island since 1964 and former Chairman of the Executive Committee of the FSC once informed me that he was one of the few people to actually spend a night in this ill-fated structure. The unhappy result was the cessation of Dale Fort’s formal connection with Skokholm.

Skok bungalow   It had been more than 20 years since my only visit to Skokholm that actually involved going ashore. We’d like to thank Richard The Warden for having us and for not blaming current Dale Fort Staff for the bungalow debacle. We hope to visit this beautiful, interesting place much more frequently in future.

 





Dale Fort Blog Number 36

5 09 2014

Stats for Twits

A simple guide to the use of hypothesis testing statistics

This blog is not a comprehensive guide to statistics. It is intended to remind/inform you of the general format and structure of hypothesis testing statistics. It does not tell how to do any actual tests.

Even if you think you know nothing about statistics, it’s almost certain that you do. You will probably have heard of terms like the “average” value or maybe the “range” of some data or possibly its “standard deviation” or “variance”. All of these things tell you something about a set of data, they are known as descriptive statistics. The statistics we are concerned with here are called hypothesis-testing statistics. For the most part you will be using them to compare one set of data with another set of data.

 

The format you follow is similar for most of these tests:

Invent a null hypothesis

Using your devastating powers of observation, you have noticed that adult humans seem on the whole to be taller than baby ones. You could easily investigate this by measuring some of each kind and comparing the average values of the two sets of data.

 

An hypothesis is simply a statement which offers an explanation of your observations. In this case our experimental hypothesis might be that all adult humans have had special cosmetic surgery to lengthen their legs and make them taller than babies. Alternatively, we might suggest that adults have been around for longer and therefore have grown bigger. Both of these would be experimental hypotheses, the latter being the more reasonable one.

 

A null hypothesis is a special sort of hypothesis which you invent purely for the purpose of doing the statistical test. It does not have to agree with your experimental hypothesis. The word null means a condition of nothingness or lacking any distinction. A null hypothesis is sometimes called an hypothesis of no difference.   It is always stated as though there were no difference between the two things you are comparing. If we were doing a test that compared our two average (or mean) heights a suitable null hypothesis would be:

   There is no significant difference between the means of the two sets of data

Remember, it might be obvious that there is a difference but you state it like this anyway. Having done the statistical test you will end up either accepting or rejecting this statement.

Calculate the value of the test statistic

All the tests do something different but the general pattern of what you do is the same. The next thing you do is use your data to calculate a value of the test statistic you are using (this will have a name, usually a letter like “t”, “U”, “rs”). You calculate a value that is specific for your data.

Find the critical value of the test statistic

Statisticians are very clever (except for Heronimous Bing of Oxford, he is thick), they have spent a long time working out what are known as critical values of test statistics for all combinations of circumstances and sets of data. You must extract from one of their tables of critical values the value that applies to your combination of circumstances. What the value is depends on the number of items of data in each data set and the degree of precision you want to use in either accepting or rejecting your null hypothesis. This is the real value of these techniques, they allow you to say how certain you are when you either accept or reject the null hypothesis. You get to choose how certain you want to be.

Here is part of a table of critical values for a statistic called Spearman’s rank correlation coefficient:

Spearman's partial table of critical values

You enter the table at the appropriate number of pairs of data (let’s say we have 9 pairs of data). The critical value lies somewhere along this row.

You will have noticed that each column is headed with a percentage significance level. This is the part where you get to pick the degree of precision or confidence you want in either accepting or rejecting your null hypothesis.

Lets us say that you wanted to be as certain as you could be (using our table above) that you would be correct in accepting or rejecting your null hypothesis. Enter the table at the 1% significance column and find the appropriate critical value by going along the 9 pairs of data row. As you can see the critical value is 0.833.

With this particular test, if the value you’ve calculated for your own data is the same or bigger than this you reject the null hypothesis. If the value for your data is smaller than the critical value you accept the null hypothesis. In accepting or rejecting it at the 1% significance level you are saying: “If I did this test a very large number of times I would expect to be correct in accepting or rejecting my null hypothesis 99% of the time. I would expect a different result due to chance only 1% of the time”. Put simply (and not quite accurately but hopefully you know what I mean): “I’m 99% certain that I’m right in accepting or rejecting my null hypothesis”.

If you are not so concerned with being near certain you can pick a bigger % significance level. If you picked the 5% level the critical value would be 0.683. This is smaller than the critical value for 1% significance and it will be easier for your value (calculated from your own data) to beat it and reject the hypothesis of no difference. However if you do it at this level you would expect different results due to chance 5% of the time. In other words 95 times out of a 100 you’d expect to be correct in accepting or rejecting your null hypothesis. 5 times out of 100 you’d expect a different result due to chance.

There is no law about what level of significance you choose but given the inherent variability of biological systems (or cussedness) it has become generally accepted that a level of 5% is acceptable for field data.

Tests you might use and what they do:

A t-test will tell you if the means of two sets of continuous data, with interval level measurements are significantly different to one another. (If you have a big sample (25+) you can use it for count data as well). Some people call it a z test when you have a big sample but we use the same formulae. For any T test you do the null hypothesis will be: There is no significant difference between the means of the 2 sets of data

A Mann-Whitney U-Test compares the medians of two sets of data and can be used on interval or ordinal data. You can also use it on data that is not normally distributed (unlike a t-test) and for as few as four pieces of data in each sample. For any Mann-Whitney U-Test you do the null hypothesis will be: There is no significant difference between the medians of the two sets of data

A chi2 test does a lot of things but for the most part we use it in a simple way to see if an observed set of data (which has to be counts of things in categories (frequencies)) differs significantly from what we might expect, given our null hypothesis. For any chi2 test you do the null hypothesis will be: There is no significant difference between the observed and the expected frequencies

Spearman’s rank correlation coefficient (snappy name eh?) will tell you whether 2 variables are correlated. I.e. Does one variable change as the other one changes? It will tell you whether the relationship is positive (both go up together) or negative (one goes up as the other goes down) and the strength of any correlation. For any Rearman’s spank correlation coefficient you do the null hypothesis will be: There is no significant correlation between the 2 variables

It conveys a much better impression that you know what you are doing if you customize the general null hypothesis to make it pertinent to your own investigation.  For example:

There is no significant difference in mean mass of customers patronizing MacSmug’s Lettuce Emporium and customers patronizing MacBloater’s Land of Grease Burger Bar

The t-test and U-test are both looking for differences between two sets of data. The chi2 test and Spearman’s rank correlation coefficient are both looking for associations between two sets of data.

Finally,  Greek letters do not seem to be catered for by this blog-host so here’s picture of what chi-squared looks like in the original Greek:chi squared

Watch out for the next blog, where we’ll live life even closer to the edge………