Quantitative Research Design Dr. Mahmoud Al-Hussami

Objectives of Presentation Describe the study designs often used. Describe how study designs can influence the validity and reliability of results. Identify the appropriate study design for the research proposal.

Research Design Refers to the outline, plan, or strategy specifying the procedure to be used in answering research questions and for testing the hypothesis. It is the formal plan for the research Researcher has to choose among presented options.

Aspects of Research Design Intervention: whether the researcher want to test effect of specific intervention. Comparison: if the researcher want to compare between certain phenomena such as: Between groups (males vs. females) Among the same group in different times (now, after 3 months, and after 6 months). Same group with different situations (type II, DM with two types of medications). Based on relative ranking ( levels of organizational commitment and salaries). Comparing with results form other study.

Aspects of Research Design (Cont.) Controlling for extraneous variables: researcher has to know a head of time what factors he need to control. Timing of data: the appropriate time and timing Site and setting: where to find the participants

Aspects of Research Design (Cont.) Communication with study participants : what information the researcher wants to share with research participants What is the Good Design? Appropriateness to the research question Lack of bias: controlling extraneous variables, or any influence that can distort the results.

Aspects of Research Design (Cont.) Precision: using precise measuring tool and controlling of extraneous variables. Power: ability of research question to detect relationship among variables.

Determinants of Choice of Study Design STUDY DESIGN The type of the problem Research Question Resources available for the study The knowledge already available about the problem

Overview of Study Types Non interventional (Observational) studies : in which the researcher just observes and analyses researchable objects or situations but does not intervene. Is descriptive in nature because there is no manipulation or control of variables The researcher must control for extraneous variables through careful selection of study sample Extraneous variables threaten the validity of the study Intervention (Experimental) Studies: In which the researcher manipulates objects or situations and measures the outcome of his manipulations. Individuals are randomly allocated to at least two groups one group is subject to an intervention, or experiment while the other groups is not. The outcome of the intervention (effect of intervention on the dependent variable/ problem) is obtained by comparing the two groups

Non Interventional (Observational Studies) Exploratory studies Descriptive studies Comparative (analytical) studies

Exploratory Studies An exploratory study is a small scale study of relatively short duration, which is carried out when little is known about a situation or problem. What areas in KSA can you have an exploratory study done? If a problem and its contributing factors are not well defined, it is always advisable to do an exploratory study before embarking on a large scale descriptive or comparative study.

Descriptive Studies A descriptive study involves the systematic collection and presentation of data to give a clear picture of a particular situation without drawing conclusion about causality Can be carried out on a small or large scale A good example is cross-sectional surveys

Cross-sectional Surveys Aims at quantifying the distribution of certain variables of interest in the study population at one point in time. They may cover Physical and Socio-economic characteristics of people. Knowledge, Attitudes, beliefs, Opinions. Events that occurred in the population Cover a selected sample of the population Census--Covers the whole population.

Cross-Sectional Studies Advantages Can study several outcomes at the one time. Researcher has control over selection of subjects. Control over measurements. Relatively short duration. Provide prevalence estimates. Step towards cohort study.

Cross-Sectional Studies Disadvantages Cannot establish temporal sequence of events (cannot determine causality) Susceptible to bias. Not ideal for rare conditions. Does not yield incidence or true relative risk.

Correlational Studies Examines the strength of relationship between variables. X is related to Y or the relationship between more than two variables. Correlation coefficient reported through statistics such as Pearson’s product-moment correlation r and or the Spearman rho. Magnitude and direction of relationship are indicated by a correlation coefficient It can be positive (+) or negative (-) and ranges between (negative to positive correlation).

Comparative or Analytical Studies Comparison is a fundamental research strategy to identify variables which help to explain why one group of persons or objects differs from another. Examines the differences between intact groups on some dependent variable of interest. Similar to experimental design but the researcher does not manipulate the independent variable (it is inherent characteristic). Attempts to establish causes or risk factors for certain problems.

Comparative studies/Cont Two types: Retrospective: (ex post facto studies or after the fact). Prospective: The independent variable is identified at the present time, and then subjects are followed in the future to observe the dependent variable. Prospective studies may use an experimental approach whereas retrospective studies would never use this type of design

Types of Analytical Studies Analytical Studies Comparative Cross- sectional Cohort studies Case control studies

Case - Control Studies In a case control study the investigator compares one group among whom the problem that he wishes to investigate is present and another group called a control or comparison group, where the problem is absent in order to find out what factors have contributed to the problem.

Case-Control Studies Time Research Cases (Have disease) Controls (Do not have disease) Yes No Yes No Exposed Exposure to Risk Factor Cases/Controls Population Source: Clinical epidemiology; Fletcher and Fletcher

Characteristics of CC studies Population at risk may be undefined Cases selected by investigator from an available pool Controls selected by investigator to resemble cases Exposure measured, reconstructed, recollected after development of disease Risk or incidence of disease cannot be measured directly.

Case-Control Studies Advantages Enable study of rare conditions (outcomes) Are of short duration Relatively inexpensive Relatively small sample sizes Allow approximation of risk.

Case-Control Studies Disadvantages Limited to one outcome variable. Susceptible to bias: Selection Measurement Survivor Cannot establish temporal sequence of events Do not yield absolute risk (incidence)

Cohort Studies In a cohort study, a group of individuals that is exposed to a risk factor(study group) is compared to a group of individuals not exposed to the risk factor (control group). The researcher follows both groups over time and compares the occurrence of the problem that he expects to be related to the risk factor in the two groups to determine whether a greater proportion of those with the risk factor are indeed affected.

Cohort Studies Cohort YES NO YES NO TIME Not exposed Exposed Population Cohort Without Disease Exposure to Risk Factor Disease Source: Clinical epidemiology; Fletcher and Fletcher Research

Cohort Studies Advantages The only way to establish incidence directly (absolute risk) Exposure can be measured without bias because outcome is not known Exposure precedes outcome (more reliable evidence of causality) Can assess multiple outcomes Can study multiple factors

Cohort Studies Disadvantages Need to follow up large numbers for rare outcome. Expensive. Results not available for a long time Assess exposures that are known at the start of the study.

Experimental Studies Individuals are randomly allocated to at least two groups. One group is subject to an intervention, or experiment while the other group is not. The outcome of the intervention (effect of intervention on the dependent variable/ problem) is obtained by comparing the two groups. Must have three elements: Manipulation of the independent variable Control: Introduce controls over the experimental situation, including the use of a control group Randomization: assignment to control and experimental groups randomly

Experimental Studies Randomised Control Trials An experimental study in which subjects are allocated to groups which do or do not receive intervention. Groups are compared for outcome. Considered gold standard design Thus subjects are enrolled on the basis of exposure Control group can be given placebo or standard treatment

Experimental Research Designs: True experimental designs Quasiexperimental designs Preexperimental designs

True Experimental Designs Studies in which the researcher has a great deal of control over the research situation. Minimal internal validity threat (The degree to which changes in the dependent variable (effect) can be attributed to the independent variable (cause)

True Experimental Designs Pretest-posttest control group O1 X O2 (experimental group) R O1 O2 (comparison group) Posttest Only Control Group O1 (experimental group) R O1 (comparison group) Solomon four-group O1 X O2 (experimental group1) O1 O2 (comparison group1) R X O2 (experimental group2) O2 (comparison group2)

Pretest-Posttest Control Group Design Characteristics: Most frequently used experimental design Controls for all threats to internal validity Disadvantages: The external threat of the reactive effects of the pretest. Results can be generalized only to situations with pretest administration before treatment

Posttest-Only Control Group Design Features of Posttest-Only Control Group X O (experimental group) R O (comparison group) Easier and superior to pretest-posttest design Random assignment of subjects into groups in the posttest-only group ensures equality

Solomon Four Group Design Subjects are randomly assigned to one of four groups: two experimental and two comparison groups. Most powerful experimental design because it minimizes threats to internal and external validity It controls for all threats to internal validity and for reactive effects of the pretest. Any differences between the experimental and the comparison groups can be more confidently associated with experimental treatment. Disadvantage of Solomon Four-Group Design Requires a large sample. Complicated analysis.

Experimental Studies Advantages Randomization distributes confounders equally between the groups to be compared for the outcome. Hence any difference can be confidently attributed to intervention. Provides evidence for cause and effect. Allows standardization of eligibility criteria, treatment and outcome assessment. Allows use of statistical tests with few in built assumptions.

Experimental Studies Disadvantages Expensive in terms of time, personnel and resources. Ethical issues for certain interventions or circumstances. May be unsuitable because of problems of likely co- operation or rarity of outcome. Tend to induce artificial situation because of Volunteerism Strict eligibility criteria Highly standardised interventions that may be different from occurs in common practice (difference between efficacy and effectiveness)

Quasi - Experimental studies In a quasi-experimental study, one characteristic of a true experiment is missing, either randomisation or the use of separate control group. Always includes the manipulation of an independent variable which serves as the intervention

Quasiexperimental designs Nonequivalent Control Group Design: O1 X O2 (experimental group) O1 O2 (comparison group) Time Series Design O1 O2 O3 X O4 O5 O6

Nonequivalent Control Group 1. It is similar to pretest-posttest control group design but with no random assignment of subjects to experimental and comparison groups O1 X O2 (experimental group) O1 O2 (comparison group) 2. Problems of this design: 1. Threats to internal validity are history, testing, maturation, and instrumentation change. 2. Biggest threat is selection bias (no one can tell if the two groups were similar to start with)

Time-Series Design 1. The researcher periodically observes or measures the subjects O1 O2 O3 X O4 O5 O6 2. assessing pain level of a group of people with low back ache over three weeks then give a specific exercise to reduce the pain. And pain level is measured again to determine if low backache still persists 3. Problems with this design: Threats to validity are history and testing

Intervention Interrupted Time Series

Preexperimental designs Types: One-Group Pretest-Posttest Design O1 X O2 Threats to internal validity: history, maturation, testing, and instrumentation change. One-Shot Case Study: X O exposure of one group to an experimental treatment and observed after the treatment.  No comparisons made  No one can tell whether they had the knowledge before the intervention  Threats to internal validity are history, maturation and selection bias