How do you determine the sample size for a case-control study?

How do you determine the sample size for a case-control study?

In case control studies, we usually calculate the odds ratio, if you are also planning to do so, your required sample size can be calculated by just putting in the values of Expected proportion exposed in controls and assumed odds ratio into the site above (link given).

What is a unmatched case-control study?

The Unmatched Case-Control study calculates the sample size recommended for a study given a set of parameters and the desired confidence level.

What sampling method is used for case-control study?

Case-base sampling (also known as “case-cohort” sampling): Controls are selected from the population at risk at the beginning of the follow-up period in the cohort study within which the case-control study was nested.

What is required in a case-control study?

REQUIREMENTS FOR SAMPLE SIZE CALCULATION BASED ON OR OR TWO PROPORTIONS FOR A CASE-CONTROL STUDY. (1) Expected OR: between exposed and non-exposed groups* (2) The probability of exposure in cases* (3) The probability of exposure in controls. (4) Statistical power: 0.8, 0.85, or 0.9.

How do you find the sample size for an odds ratio?

This is the minimum sample size you need in the absence group to estimate the true population odds ratio with the required relative precision and confidence level. Multiply this number by the sampling ratio to calculate the sample size for the presence group.

What is odds ratio in case-control study?

The odds ratio is the “measure of association” for a case-control study. It quantifies the relationship between an exposure (such as eating a food or attending an event) and a disease in a case-control study. The odds ratio tells us how much higher the odds of exposure are among case-patients than among controls.

How do you interpret odds ratio?

Odds Ratio is a measure of the strength of association with an exposure and an outcome.

1. OR > 1 means greater odds of association with the exposure and outcome.
2. OR = 1 means there is no association between exposure and outcome.
3. OR < 1 means there is a lower odds of association between the exposure and outcome.

How do you calculate odds ratio in case-control study?

The odds ratio is calculated using the number of case-patients who did or did not have exposure to a factor (such as a particular food) and the number of controls who did or did not have the exposure. The odds ratio tells us how much higher the odds of exposure are among case-patients than among controls.

How do you calculate odds of exposure among cases?

In a 2-by-2 table with cells a, b, c, and d (see figure), the odds ratio is odds of the event in the exposure group (a/b) divided by the odds of the event in the control or non-exposure group (c/d). Thus the odds ratio is (a/b) / (c/d) which simplifies to ad/bc.

What does the odds ratio estimate in a case-control study?

The odds ratio is the measure of association for a case-control study. It tells us how much higher the odds of exposure is among cases of a disease compared with controls. The odds ratio compares the odds of exposure to the factor of interest among cases to the odds of exposure to the factor among controls.

How are odds ratios calculated?

The odds ratio is calculated by dividing the odds of the first group by the odds in the second group. In the case of the worked example, it is the ratio of the odds of lung cancer in smokers divided by the odds of lung cancer in non-smokers: (647/622)/(2/27)=14.04.

What do you need to know about unmatched case control?

Unmatched Case-Control. The Unmatched Case-Control study calculates the sample size recommended for a study given a set of parameters and the desired confidence level.

How to use StatCalc for unmatched case control?

From the Epi Info™ main page, select StatCalc. Select Unmatched Case-Control. The Unmatched Case-Control window opens. Select the Two-sided confidence level of 95% from the drop-down list. Enter the desired Power (80%) to detect a group difference at that confidence level. Enter the ratio of controls to cases as 3.

How to use unmatched case control in Epi Info?

The application will show three different sample size estimates according to three different statistical calculations. From the Epi Info™ main page, select StatCalc. Select Unmatched Case-Control. The Unmatched Case-Control window opens. Select the Two-sided confidence level of 95% from the drop-down list.