Mpembeni RNM, SPHSS, MUHAS VARIABLES

Definitions (1) What is a variable? A variable is any aspect of your study unit that is measured. An attribute or characteristic of a person (or object) that can change from person to person. Eg Age, SBP, FP use, Birth weight etc Each of these characteristics varies from person to person A VARIABLE MUST VARY!!!  If (hypothetically), in a group of 200 persons, each person has black hair and black eyes:  Hair colour and eye colour could NOT be variables

Educational Research 2e: Creswell What is a Variable? A Variable (A Characteristic or Attribute) That can be Measured and Varies (Can be assessed on an instrument and recorded on an instrument) (Can assume different values or scores for different individuals)

Definitions Some variables can be measured straight from the study subject Eg Age Height HIV Sero status FP use Awareness of PMTCT

Definitions Some variables are complex can not be measured straight May be broken up to components which can be regarded as separate variables and measured separately. Eg Knowledge of HIV transmission, attitude towards Rape Quality of care Satisfaction with services Quality of life etc

Measurement Some variables can be converted into indicators eg birth rates, death rates, prevalence rates etc

Dependent/Independent Variables When association between two variables is studied, the variables may be referred to as dependent and independent. The Dependent (AKA Outcome) variable is the variable that is the focus of the study- the main outcome measure An outcome of interest that is measured by the researcher The variable whose occurrence or variation we are seeking to understand A variable that might be affected by a change in another variable OR a variable that is hypothesized to be affected by the IDs

DEPENDENT VARIABLES Examples Use of FP methods HIV serostatus among secondary school students Nutritional status of children aged under 5 years Disclosure status among HIV positive women age Knowledge of health care workers on management of eclampsia Birth weight among babies born in hospital y Quality of health care Quality of life among patient with CA prostate Adherence to ART

Dependent Variable The type of the outcome variable determines the most important statistical methods in: Sample size calculation Data analysis

INDEPENDENT VARIABLES AKA Explanatory variables Variables which are thought to influence the outcome variable. We normally look for factors/exposures that may influence the occurrence of the outcome variable We try to see if and how much the IV influences the DV

Selection of Variables What variables should I include in my research study? Variables are based on the objectives of the study Key variables are normally mentioned in the objectives Some variables may not be mentioned in the objectives but require to be measured if the study is to attain its aims eg the socio demographic characteristics for studies dealing with human subjects Eg. Sex, age, education level, marital status, occupation, place of residence, religion? Ethnicity? etc Time/date the event occurred

Other Variables Confounding Variables (Spurious Variables) They may influence the relationship between the independent and the dependent variable. Interfere with the ability to study the relationship between the IVs and the DV because it is another causal variable that might be influencing the DV These should always be included

Number of Variables How many variables do you need? As many as necessary and as few as possible Only collect data for the variables you will need in your analysis. The common practise is to collect information on too many variables and most of the data may not be analysed.- This is unethical Making of dummy tables at this stage may help to check on the list of your variables

Clarify your variables Variables to be measured should be clarified at the proposal writing stage. Formulate an operational definition of the variable eg a case definition, units of measurement, measurement scale etc This should be done to avoid ambiguities at the time of data collection and analysis

For Tomorrows Plenary Prepare Your Study Title Objectives Study Design and data collection methods List of variables: Dependent and Independent Variables