Sample is a part of the population.
Q: Why should we draw a sample from the population?
A: Because the population is too large and should be reduced to enable investigation.
Types of Sampling
1. Probability sampling
We draw the sample randomly. This type of sampling is used in quantitative research, but never used in qualitative research.
a. Simple random sampling
It means everybody has an equal chance of being selected as a sample. You draw the sample by choosing individual students randomly. For example, you have 100 students in the population so write the students' names on 100 small pieces of paper. Fold the pieces of paper and put them in a bowl. Shake the bowl, then take 30 pieces of paper randomly from the bowl. Now you have 30 students as the sample of your study.
b. Stratified sampling
The population is divided into several strata/levels, then the sample is drawn from each level. For instance, you want to conduct research at SMAN 5. There are three grades: the 10th grade, the 11th grade and the 12 grade. These grades are the levels, which can be used as a basis to draw the sample. List the number of the students from the highest to the lowest level, then draw a sample from each level.
c. Cluster sampling
The population is divided into several clusters/groups, then a sample is drawn from each group. For example, you want to conduct research to the tenth graders. If there are five classes (clusters), list the number of the students in these classes and draw a sample from each class.
d. Systematic sampling
The sample is drawn by selecting the n-th person in the population. For example, there are 150 students in the population and you need 30 students in your sample. Divide the number of students in the population (150) by the number of students in the sample (30), you get 5.
150 : 30 = 5
It means you could draw the sample by choosing every 5th student in the list.
2. Non-probability sampling
We do not draw the sample randomly. It is used in qualitative and quantitative research.
a. Accidental sampling
Choosing any person that you meet as the sample.
b. Purposive sampling
Selecting a sample from the population for a particular reason. This is used in qualitative research, but not quantitative research. For example, you conduct research to find out the strategies of proficient readers in comprehending a narrative text. You need to draw a sample from a reading class, and choose 8 proficient readers by taking the teacher's judgement into account. Ask the reading teacher which students are proficient readers, then you could select 8 out of several students mentioned by the teacher.
c. Quota sampling
Dividing the population into levels, then selecting n % from each level. For example, you list the 11th graders belonging to programs A1, A2, A3 and A4. Because the number of students in these programs varies, it is better to use quota sampling by taking 10% of students in each program as your sample.
mom, I have two questions, the first is "can you tell me the steps before we get the result of t test? and the second is how do I count the student responses?give me the formulas?thank u so much.umi alimatus s (your student in research class)
ReplyDeleteTo compute t value using t-test, you can use MS excel, it's easier than using a calculator. To interpret the results, you can read about it in the statistics book by Bartz (I use the book in my statistics class, your friends who attended my classes should have a copy of the book).
ReplyDeleteTo count the students' responses, you can use percentage analysis, e.g. how many percent of the students think that the materials are interesting, etc.