A Survey is a study of one or more characteristics of a group. A Survey is a study of one or more characteristics of a group.

Population vs. Sample The entire group of individuals that we want information about is called the population. The entire group of individuals that we want information about is called the population. A sample is a part of the population that we actually examine in order to gather information. A sample is a part of the population that we actually examine in order to gather information.

Example: Let’s say we want to find the average height of female students at HHS. It is too much trouble to try to measure the height of each girl, so we go to 20 different homerooms and measure the height of 5 girls in each of those homeroom. Example: Let’s say we want to find the average height of female students at HHS. It is too much trouble to try to measure the height of each girl, so we go to 20 different homerooms and measure the height of 5 girls in each of those homeroom. The population of our study is “Females at HHS”. The population of our study is “Females at HHS”. The sample of the study is the group of 100 girls whose height we actually measured. The sample of the study is the group of 100 girls whose height we actually measured.

Sample Design is the term used to describe the method used to choose the sample from the population to survey. Sample Design is the term used to describe the method used to choose the sample from the population to survey. There are many ways to choose a sample. Some methods are more preferred than others. There are many ways to choose a sample. Some methods are more preferred than others.

Self-selected Sample This methods allows the sample to choose themselves by responding to a general appeal (volunteering to be surveyed). This methods allows the sample to choose themselves by responding to a general appeal (volunteering to be surveyed). Examples of Self-selected Sample: a call-in radio poll, an internet poll on a website Examples of Self-selected Sample: a call-in radio poll, an internet poll on a website Problems with Self-selected samples: bias – because people with strong opinions on the topic (especially negative opinions) are most likely to respond. Problems with Self-selected samples: bias – because people with strong opinions on the topic (especially negative opinions) are most likely to respond.

Convenience Sampling In a convenience sample individuals are chosen because they are easy to reach. In a convenience sample individuals are chosen because they are easy to reach. Example: People conducting a survey go to the mall and stop people who are shopping. This is convenient for the person doing the survey but does not guarantee that the sample is representative of the population of the study. Example: People conducting a survey go to the mall and stop people who are shopping. This is convenient for the person doing the survey but does not guarantee that the sample is representative of the population of the study. Convenience sampling also involves bias on the part of the interviewer. Convenience sampling also involves bias on the part of the interviewer.

Random Samples A random sample of size n individuals from the population chosen in such a say that every set of n individuals has an equal chance to be the sample selected. A random sample of size n individuals from the population chosen in such a say that every set of n individuals has an equal chance to be the sample selected. Example: Putting everyone’s name in a hat and drawing 3 names to participate in the study. Example: Putting everyone’s name in a hat and drawing 3 names to participate in the study.

Systematic Sample When a rule is used to select members of the population. When a rule is used to select members of the population.

Stratified Random Sample To select a stratified random sample, first divide the population into groups of similar individuals, called STRATA. Then choose a separate sample in each strata and combine these to form the full sample. Common example would be separating by gender or race first, then selecting samples from each group.

Representative Sample A sample that accurately reflects the characteristics of a population. A sample that accurately reflects the characteristics of a population. This is what we want! This is what we want!

Sample Bias A biased sample is a sample that is NOT representative of the population. A biased sample is a sample that is NOT representative of the population. Example: if we are trying to find out something about students at HHS and we include students for KMHS in our survey then we’ve included people who are not in our population. Example: if we are trying to find out something about students at HHS and we include students for KMHS in our survey then we’ve included people who are not in our population.

Question Bias A question that is worded in such a way to encourage a particular response is a biased question. A question that is worded in such a way to encourage a particular response is a biased question.