ITFT- Sampling

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Information about ITFT- Sampling
Education

Published on April 26, 2014

Author: sl22

Source: slideshare.net

Description

Sampling is the process of selecting units from a population.

SAMPLING METHODS

What exactly IS a “sample”?

What do qualitative researchers worry about? I want to see the world through the eyes of my respondents. I want to describe the context in a lot of detail. I want to show how social change occurs. I’m interested in how things come to be. I really want my research approach to be flexible and able to change.

Social actors are not predictable like objects. Randomized events are irrelevant to social life. Probability sampling is expensive and inefficient. Non-probability sampling is the best approach.

Types of samples

Simple Random Sample  Get a list or “sampling frame” a. This is the hard part! It must not systematically exclude anyone.  Generate random numbers  Select one person per random numbers

Systematic Random Sample  Select a random number, which will be known as k  Get a list of people, or observe a flow of people (e.g., pedestrians on a corner)  Select every kth person  Careful that there is no systematic rhythm to the flow or list of people.  If every 4th person on the list is, say, “rich” or “senior” or some other consistent pattern, avoid this method

Stratified Random Sample 1. Separate your population into groups or “strata” 2. Do either a simple random sample or systematic random sample from there a. Note you must know easily what the “strata” are before attempting this b. If your sampling frame is sorted by, say, school district, then you’re able to use this method

Multi-stage Cluster Sample  Get a list of “clusters,” e.g., branches of a company  Randomly sample clusters from that list  Have a list of, say, 10 branches  Randomly sample people within those branches  This method is complex and expensive

The Convenience Sample Find some people that are easy to find

The Snowball Sample  Find a few people that are relevant to your topic.  Ask them to refer you to more of them.

The Quota Sample  Determine what the population looks like in terms of specific qualities.  Create “quotas” based on those qualities.  Select people for each quota.

The Theoretical Sample

Accidental sampling • A type of nonprobability sampling which involves the sample being drawn from that part of the population which is close to hand • The researcher using such a sample cannot scientifically make generalizations about the total population • In social science research, snowball sampling is a similar technique

Panel sampling • The method of first selecting a group of participants through a random sampling • Period of data collection is called a "wave“ • Panel sampling can also be used to inform researchers about within-person health changes due to age

How many? Qualitative researchers seek “saturation” • “How many” isn’t the issue. Do you understand the phenomenon? Have you learned enough? • Mere numbers are irrelevant. You want “verstehn” or deep understanding Quantitative researchers seek statistical validity • Can you safely generalize to the population? Have you systematically excluded anyone? (See the “famous sampling mistake”)

Improving Response Rates • Personalize the invitation • Offer money -- no strings attached

Thank You

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