Sampling Methods in Qualitative and Quantitative Research

Sampling in Qualitative and Quantitative Research A practical how-to

Key themes• A famous sampling mistake• Quantitative assumptions in sampling• Qualitative assumptions in sampling• Types of sampling• Ethnographic sampling• Interview sampling• Content analysis sampling• How many?

A famous sampling mistake

A famous sampling mistakeThat’s Truman They only asked rich, white people with telephones who’d they vote for. Sadly, they published their mistake

Even with proper sampling…beware! “…predicting behavior on the basis ofknowledge of attitude is a very hazardous venture.” Meaning, predicting socialbehavior is often misguided. Keep that in mind!

What exactly IS a “sample”?

What exactly IS a “sample”? A subset of the population, selected byeither “probability” or “non-probability” methods. If you have a “probabilitysample” you simply know the likelihood of any member of the population being included (not necessarily that it is “random.”

What do quant researchers worry about? I really spend a lotI want to know what of time wondering I want to make surecauses something how to measure I wonder how small others can repeatelse. things. patterns generalize to big my findings. patterns.

Assumptions of quantitative samplingWe want to generalize to thepopulation. Random events are predictable. We can compare random events Therefore… to our results. Probability sampling is the best approach.

What do qual researchers worry about?I want to see the I want to describe I really want myworld through the the context in a lot I want to show how research approacheyes of my of detail. social change occurs. I’m to be flexible andrespondents. interested in how things able to change. come to be.

Assumptions of qualitative samplingSocial actors are not predictablelike objects. Randomized events are irrelevant to social life. Probability sampling is expensive Therefore… and inefficient. Non-probability sampling is the best approach.

Types of samples

Simple Random Sample1. Get a list or “sampling frame” a. This is the hard part! It must not systematically exclude anyone. b. Remember the famous sampling mistake?2. Generate random numbers3. Select one person per random number

Systematic Random Sample1. Select a random number, which will be known as k2. Get a list of people, or observe a flow of people (e.g., pedestrians on a corner)3. Select every kthperson a. Careful that there is no systematic rhythm to the flow or list of people. b. If every 4th person on the list is, say, “rich” or “senior” or some other consistent pattern, avoid this method

Stratified Random Sample1. 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 Sample1. Get a list of “clusters,” e.g., branches of a company2. Randomly sample clusters from that list3. Have a list of, say, 10 branches4. Randomly sample people within those branches a. This method is complex and expensive!

The Convenience Sample1. Find some people that are easy to find

The Snowball Sample1. Find a few people that are relevant to your topic.2. Ask them to refer you to more of them.

The Quota Sample1. Determine what the population looks like in terms of specific qualities.2. Create “quotas” based on those qualities.3. Select people for each quota.

The Theoretical Sample

What about generalizing?“Our findings have a margin of “The average man is 35% moreerror of + or - 4%, 19 times out likely to choose this option of 20.” over the average woman.”

Proviso in non-probability sampling: no generalizing“Our findings have a margin of “The average man is 35% moreerror of + or - 4%, 19 times out likely to choose this option of 20.” over the average woman.”

Ethnographers sample…People Places Contexts Times Events

Interviewers sample…People Places Times

Content analysts sample… Media Dates

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!

Copernicus ConsultingDesign research and strategy http://www.copernicusconsulting.net

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Sampling Methods in Qualitative and Quantitative Research

by Sam Ladner

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