Statistics

Cohort studies

A long period of time

A sample is a subset of the population that is being studied.

A sample

Systematic sample is obtained by selecting every kth individual from the population. This first individual select correspond to a random number between 1 and k

A systematic

An individual is a person or object that is a member of the population being studied

An Individual

Bias if the result of the sample are not representative of the population , then the sample has bias.

Bias

Case control studies

Called retrospective, to look back in time

A cluster sample is obtained by selecting all individual within a randomly select collection or group of individuals.

Cluster

Controll nonresponse by using callbacks, rewards and incentives. Reward such as cash payment for completing a questionnaire. Incentive include cover letter ..

Controll nonresponse

Convenience sample is a sample in which the individual are easily obtained and not based on randomness

Convience sample

Descriptive statistics consist of organizing and summarizing data through numerical summaries, tables and graph. Inferential statistics use method that take a result from a sample, extend it to the population, and measure the reliability of the result.

Descriptive and Inferentive Statistics

Discrete variable is a quantitative that has either a finite number of possible values or a countable number of possible values. 0,1,2.... Continuous variable is a quantitative variable that has an infinite number of possible values that are not countable

Discrete variable and Continuous variable

Frame lists all individual in a population

Frame

Heterogeneous different, when each cluster is heterogeneous , fewer cluster with more individual in each cluster are appropriate

Heterogeneous

Homogeneous dong nhat, similar. If the cluster have homogeneous individuals, it is better to have more clusters with fewer individuals in each cluster

Homogeneous

Cross sectional studies

In a specific time, very short of period of time

Nominal: name, label , categorize . Does not allow arranged in a ranked, specific order exp: gender Ordinal: name, label and allow arranged in a ranked or specific order. Exp: Social class such as upper class, middle class and working class. Interval: can be rank - ordered. Zero does not have mean. Exp: a scale is temperature, time of a day on 12 hour- clock Ratio: like interval but zero has means . Exp GPA, number oc children

Nominal level of measurement Ordinal level of measurement Interval level of measurement Ratio level of measurement

Nonresponse bias exists when individual select to be in the sample do not respond to the survey have different opinion from those who do. Do not respond or the interview was unable to contact them

Nonresponse bias

Population is the entire group of individual to be studied

Population

Qualitative or categorical variables allow for classification of individual based on some attribute or characteristic Quantitative variables provide numerical measures of individual. Arithmetic operations such as addition ans subtraction can be performed on the values of a quantitative variable and will provide meaningful results.

Qualitative and quantitative Variables

Random sampling

Random sampling is the process of using chance to select individual from a population to be included in the sample

Response bias exist when the answer on a survey do not reflect the true feelings of respondent. Reason of response bias such as interview error , misrepresented answer, wording of questions

Response bias

Statistics is the science of collecting, organizing, summarizing and analyzing information to draw conclusions or answer questions. In addition, statistics is about providing a measure of confidence in any conclusions.

Statistics

Statistics -Parameter Statistic is a numerical summary of a sample. S-S Parameter is a numerical summary of a population. P-P

Statistics -parameter

Stratified sample is obtained by separating population into strata and then obtaining a simple random from each strata. The individual within each strata should be homogeneous or similar in some way.

Stratified and strata

Undercoverage occurs when the proportion of one segment of the population is lower in a sample. Undercoverage can result because the frame used to obtain the sample is incomplete or not representative of the population.

Undercoverage