Population- The set of all things that you are interested in.
Sample- A subset of the population.
Parameter- A numerical measure of a population (e.g. mean/ standard deviation).
Statistic- A numerical measure of a single sample; one or more statistics can be used to estimate the population.
Biased- If the resulting sample is not representative of the population.
(Question) “Give a reason why this sample is not a random sample.”
(Answer) Not all subsets are possible.
Simple Random:
Method:
Assign a number to each member of the population using a full list of the population.
Generate a list of random numbers using a random number generator.
Choose the corresponding members for your sample.
Ignore any repeats/ numbers outside the range.
Positives:
Every member of the population has an equal chance of being selected - so this method is completely unbiased.
Negatives:
May be inconvenient if the population is spread over a large area (as it would be difficult to locate & contact the selected members).
Stratified:
Method:
Divide the population into categories (called ‘strata’).
Calculate the total population.
Calculate the number needed for each category in the sample using:
4. Select the sample for each category using the simple random sampling method.
Positives:
Useful when results may vary depending on the strata.
Representative (if the population has clearly distinct categories).
Negatives:
May be inconvenient if the population is spread over a large area (as it would be difficult to locate & contact the selected members).
Systematic:
Method:
Assign a number to each member of the population using a full list of the population.
Calculate a regular interval to use by dividing the population size by the sample size.
Generate a random starting point that is less than or equal to the size of the interval. The corresponding member of the population is the first member of the sample.
Continue adding the interval to the starting point to select the remaining sample members.
Positives:
This method can be used for quality control on a production line.
Should give an unbiased sample.
Negatives:
Regular intervals may coincide with a pattern.
Cluster:
Method:
Split the population into clusters that you expect to be similar to each other.
Take a sample from some of these clusters at random.
Positives:
Quick and economic/inexpensive to gather a sample.
Negatives:
Not representative of the population.
More likely to be a biased sample.
REMEMBER: Categories/Strata are groups that you expect to be different (e.g. year groups in school) but Clusters are groups you expect to be similar (e.g. different classes in the same year group).
Opportunity:
Method:
The sample is chosen from a section of the population that is convenient for the sampler.
Positives:
Very quick.
Very easy.
Negatives:
Not random so very biased (no attempt to make it representative).
Quota:
Method:
Divide the population into categories.
Give each category a quota (number of members to sample).
Collect data until the quotas are met in all categories without using random sampling (usually opportunity).
Positives:
Interviewer continues until quotas are met so non-response is less of a problem.
Does not require a full list of the population.
Negatives:
Can be easily biased by the interviewer.
Not a random sample.
Avoid sample bias by:
Randomly selecting a sample.
Ensure all sample members respond.
Select from correct population & include everyone.
Day 20/100 of 100 Days of Productivity! (28/03/18) 📒📑 Firstly, apologies for the late posting; I got caught up with writing! Ahem. Today, I continued self-teaching Biology Topic 17 & 18, as well as making revision notes on Hydrogen fuel cells for Chemistry. I also finally retrieved the sheet music to begin learning “The Days That’ll Never Come” by Yiruma. On a different, more serious note, today we got back our final prep exams for Maths. Until we did them, I had been ritualistically, almost, doing 3-5 practice questions a day, and going over things I wanted to do better in. In my entrance exam, I got a very low B, but considered I got a D at the end of Year 10, I was very happy with that. My ultimate goal was to get an A in these exams, but unfortunately, my total only came to 165, which was 3 marks away from the A grade boundary (168). I know I shouldn’t be beating myself up over it, but I am quite disappointed. If anyone can help, please please send in advice on how to boast marks on anon-Calculator papers! It seems to be that that’s where I’m losing the most marks and it’s costing me grades...! (Sorry for the depressing post. I’ll be better tomorrow hopefully!!) 🎵 With Ears To See And Eyes To Hear ~ Sleeping With Sirens 🎵
april study challenge day 30: how did april treat you?
even if april wasn't as productive as i may have hoped, i did have a good month. i’m also proud that i managed to post something for every day of this challenge (even if they weren't always on time!)
Day 24/100 of 100 Day of Productivity! (01/04/18) 🔭📚
Happy Easter and April Fools’ Day to everyone! I hope you had a good day!! I was much more productive than I thought I’d be today, which is good! To begin with, I completed a few practice questions for the Calculator Maths Paper 2. Then, I made notes on The Solar System and Life Cycle of a star, which are the triple topics we’ve kind of been rushing through in school. (Also I apologise for my horrific drawings of stars - art is not my forte I’m afraid.) After this, I went back and redid the question from my Paper 2 final Maths mock with the help of another wonderful studyblr!! Finally, I began to go through the Psychology paper 1 case studies in detail, highlighting key points and writing down the evaluations.
I also feel like I should clarify now that I am travelling to Berlin, Germany for 5 days on Tuesday, and whilst I will be taking revision with me, I apologise if posts are a day late or so as I’m not sure if my hotel has WiFi. But I will definitely stay productive throughout the holiday! ✨
Day 22/100 of 100 Days of Productivity! (30/03/18) 📔✨ Today was very productive thankfully! Despite the fact I went out with my sister and got soaked early, I managed to make notes on lessons 18.3 and 18.4 for Biology, as well as getting some more reading on drug classes and narcotic controls. I also completed an entire non-calculator practice paper for Maths. I didn’t really struggle this time because it was the old specification and the questions were a lot easier to understand. It does help my confidence with Maths when I manage to do things! Finally, my piano grade 4 books arrived!! I was going to be doing the grade 3 exam since that was what I’d worked for, however the summer exams are in the midst of my GCSEs so I can’t do that, and will now complete grade 4 in November! 🎵 Never Enough ~ The Greatest Showman (soundtrack) 🎵
《 24th Feb 2018 》
—
→ Had a university workshop today, which took up the majority of my day.
→ I did a couple hours worth of maths homework (still haven’t finished😓)
→ Listened to Beethoven’s 3rd symphony🎶 in the meanwhile: I was reading a manga called “Nodame Cantabile” which referenced it.
→ Ft. a view from my window 🌇
