Analogous estimating, also known as top-down estimating, involves using the data of previous, similar projects as the basis for estimating the cost, duration or effort of the current project. It is most reliable when the previous projects are similar in fact and not just in appearance, and the individuals preparing the estimates have the needed expertise. Though it is not as accurate as other methods, it is less costly, and less time consuming which makes it a perfect choice for a quick or high-level overview of the project.

Parametric estimating involves using statistical modeling to make predictions. In this method, characteristics of the project (parameters) are represented in a mathematical model to predict project costs, resources, duration etc. The accuracy of the model depends on the quality and relevance of the data used. This method works best when the project parameters are quantifiable and can be reliably forecasted through the model. For instance, cost per square foot to build a commercial building.

Three-point estimating is a technique that uses statistical analysis to arrive at a project estimate. It uses three estimates to define an approximate range for an activity’s cost: the most optimistic cost (best-case scenario), the most pessimistic cost (worst-case scenario) and a most likely cost scenario. Confidence levels and standard deviation are then used to create a probability distribution (usually a PERT distribution) for the overall project estimate.

As the name implies, bottom-up estimating starts at the lowest level of the Work Breakdown Structure (WBS) and moves upwards to calculate the total estimate. This method gives a detailed and accurate estimate because it identifies costs at the task level. Though time-consuming and resource-intensive, it gives a thorough understanding of where the project costs are going, and can hence be used to justify costs to stakeholders.

Expert judgement is another commonly used technique in project estimation. This technique relies on input from knowledge area experts, whether it's industry experts, stakeholders, or the project team. These experts help to estimate resources, costs, duration etc. based on their experience from previous projects. This method can be remarkably accurate, especially when experts have substantial experience with similar projects. However, it is also influenced heavily by the quality of the expert input and can oftentimes be subject to biases.

Top-Down Estimating technique is often used at the initial stages of a project for getting a rough estimation of costs and timeframes. The estimations are made based on the overall project’s tasks and objectives, often leveraging historical data for similar projects. The project is then divided into smaller tasks and their costs and durations are estimated from the total cost and duration. The main advantage of the approach is its simplicity and speed. However, the drawback is that it does not consider factors such as resource availability and dependencies between tasks, sometimes leading to inaccuracies in the estimates.

Reserve Analysis is a technique used to account for potential uncertainties in project estimates. In this method, additional resources, known as 'reserves', are included in the project cost and schedule estimates to mitigate risks. There are two types of reserves; contingency reserves and management reserves. Contingency reserves are estimated to account for identified risks, while management reserves are set apart to address unforeseen risks. This technique helps in managing the uncertainties and risks associated with the project.

Cost of Quality estimation technique is an approach to predict the costs related to ensuring the quality of the project outcomes. These costs include prevention costs (the costs to prevent the failure), appraisal costs (the costs to assess the quality), internal failure costs (costs incurred to fix the issues before the product reaches the customer), and external failure costs (costs incurred after the product reaches the customer). The objective of these estimates is to identify the best balance of costs to achieve the desired level of quality.

Vendor Bid Analysis is an estimation approach used when outsourcing a part of a project to vendors. The vendors are asked to provide a quote or bid for their part, and these bids are then analyzed to choose the best vendor. The vendor bids may also be used to estimate the cost of the part of the project being outsourced. This helps the project team control costs and ensure a fair and competitive process.

Heuristic estimation technique is predominantly rooted in the past experience, historical data, and expert knowledge of the project team and key stakeholders. It’s a rule-of-thumb method that provides an approximation. For example, a development team may have a rule that they can develop 5 features per day. This generalized estimate may not be accurate in all instances, as the size and complexity of features can vary, but it can still be useful for creating quick initial estimations.

The Function Point estimating technique is a method of measuring the functionality delivered by the project. Function points are a unit measure for software much like an hour is to measuring time. They quantify software functionality provided to the user based primarily on the logical view. What sets apart this estimation technique is its standard rules and guidelines, which make it an increasingly credible, reliable and efficient in measurement and analysis.

The Delphi technique is a consensus-oriented estimating approach. In this method, experts in the particular field anonymously fill out questionnaires to address complex problems, predict results, or determine solutions. These results are compiled and shared with the group, following which the process is repeated, taking into consideration the collective responses, thus moving towards a 'group consensus estimate'.

The Program Evaluation and Review Technique (PERT) is a statistical tool used in project management to represent tasks or activities and their relationships. A PERT estimate is calculated as (Optimistic + (4 X Most Likely) + Pessimistic) / 6. This technique is useful when activities do not follow the normal distribution and where impressionistic estimates are risky.

The Monte Carlo Simulations is a quantitative risk analysis technique used in identifying the risk level of achieving objectives. This technique provides a range of possible outcomes for each risk factors and calculates the probability of completing the project on time or within budget. It involves running a risk model several times to simulate a variety of possible scenarios. It then uses statistical techniques on the collected data which is signified in a graph.