Quantitative Research Deals with quantities and relationships between attributes (variables). Involves the collection and analysis of highly structured data in the positivist tradition. Appropriate in the situations of pre-existing knowledge. Using standardized data collection methods. Aims to test hypotheses or document prevalence.

Survey A method of collecting information, from a sample of the population of interest, usually by personal interviews, postal or other self- administered questionnaire, or diaries. Survey can be carried out at one point of time (cross-sectional or retrospective surveys) or at multiple points in time (longitudinal surveys). Survey  Census

Objectives of Survey To estimate certain population parameters of interest, using statistics calculated from the data derived from the study sample. To test a statistical hypothesis about a population of interest.

Descriptive vs. Analytic Survey Descriptive survey is designed to measure certain phenomena in the population of interest (cross-sectional or retrospective survey). Analytic survey aims to investigate causal associations between variables in the population of interest (longitudinal or prospective survey).

Limitations of Descriptive Survey Can’t provide robust evidence about the direction of cause and effect relationship, therefore, can’t be used to impute causality (associations only). Potential for selectivity in recall. Recall bias

Advantages of Descriptive Survey Widely used in social sciences and epidemiological studies. Save time and resources. Standardized data are easily coded.

Analytic Longitudinal Survey Survey takes place over the forward passage of time with more than one period of data collection. Panel survey (follow-up of the same population over time) Cohort study (follow-up samples share a common characteristic or experience) Trend survey (different samples at each data collection period)

Cohort Study Cross-sectional and retrospective Collection of data at one point in time about the past Longitudinal and retrospective Collection of data at more than one point in time about the past Longitudinal and retrospective Collection of data at more than one point in time over the forward passage of time

Requirements of Longitudinal Study Careful definitions of study group. Careful selection of variables. Data collection at frequent time intervals. High response rate. Sample attrition due to death, relocation and refusal over time must be minimized. Set the timing of repeated survey points logically. The use of sensitive instruments.

Idea of Triangulation Methodological triangulation Data triangulation Theory triangulation Measurement triangulation

Types of Changes The real change overtime (  change) The scale of values which participants use to make judgment has changed (  change) Participants’ conceptualization of target variable has changed (  change)

Effect Size Estimate of the magnitude of change Difference between the after and before scores Difference between mean scores at assessments, divided by the SD of baseline scores Difference between mean scores at assessments, divided by the SD of change scores

Sample Attrition (Healthy Survivor Effect) The most vulnerable and ill subjects will died or dropped out gradually, leaving healthy subjects in longitudinal study, and lead to biased results